Ed covered this pretty well, but I wanted to elaborate a bit more on the multiple-dues-levels idea, and some thoughts and observations from experience.
Portray dues as tit-for-tat payment for a service at your peril. To put it in "Predictably Irrational" terms, when people apply market norms to a situation, they become very value-minded, and want to feel like they're getting their money's worth, getting a bargain, etc. That's sensible, but it means that when people aren't around the space very much, they'll want to drop their membership because they're not getting much use out of it. Try to keep things in the social sphere, so members focus on the group's overall goals, the social good their dues are accomplishing, and the warm-fuzzy feelings of supporting something that furthers goals they find worthy. Members should feel proud to support the group whether they set foot in the building during a particular month or not. (There will always be some absentee members, for various life reasons. They can still be strong advocates and supporters from afar, if you structure it right.) 
We did one thing right, which was to offer multiple dues levels, to accommodate people who could only afford so much, while allowing folks who could afford more to contribute financially at a higher level. This worked pretty well when the system was first devised. However, we felt that we needed to differentiate the levels somehow, so we decided that the $89 members got a vote but the $39 members didn't, and the $89's got unlimited use of the large tools whereas the $39's were supposed to explore but not make heavy use of the large tools. (We also considered offering member storage, versus having to take your project home every night, as a differentiating factor, but ultimately decided it would be too much administrative overhead.) As time went on and more members joined, the nuances weren't adequately explained, and a lot of people thought of the affordable-tier memberships as "less valued", and this contributed greatly to, ahh, how to say it... member disharmony? 
In retrospect, I think this makes perfect sense. Communication in our group is less than perfect, and without a strong message to reinforce the warm-fuzzy everyone-is-valued aspect, people saw a differentiation of payment, a differentiation of services, and applied market logic to the situation. It's no surprise that people who didn't feel like they needed the vote would drop their memberships to the lower level even if they could absolutely afford more, because they saw it as payment for a service they weren't using. Also, a lot of people (it turns out, after some careful survey work) perceived much greater differences between the two levels than there factually were. Still can't figure out where those ideas came from, but people held them and acted on them.
We ended up discontinuing the two-level concept, and going to a single unified dues level, because we were financially able to, and because it was easier than re-educating a bunch of not-very-connected-in-the-first-place members. (I mean, in practice, if folks had gotten the wrong idea already, there was clearly a communication mismatch somewhere. Fixing nuance through the same already-dysfunctional channels just wasn't gonna happen.) This is my fault as much as anything -- I underestimated the difficulty of sharing a nuanced vision with dozens of individuals.
If I had it to do again, I'd recommend having a whole lot of closely-spaced dues levels. Maybe $10, $20, $30, $40, $50, $60, $70/mo or something. The lower ones wouldn't necessarily include a key (which means that people contributing at that level wouldn't have to endure the substantial keyholder orientation), but otherwise I'd make it clear that they're exactly equal and the only difference is how much support you feel you can give to the group. Emphasize the notion that dues aren't tit-for-tat payment, but rather, an ongoing contribution of support for the group and its goals and the social good that comes from it, regardless of whether any given member is able to come to the physical space very often. I think if that's clear from the beginning, you could sidestep some of the perceived-inequality troubles we had.
And emphasize the heck out of the "ongoing" notion -- I can't overstate the importance of recurring automatic payments. If the default action when someone does nothing, is that you don't get dues, you've got something set up wrong -- make it automatic, incentivize that, profusely thank people who ease the group's overhead in this way, etc. If you're writing or integrating membership-management software, I think the single most important feature, for the financial health of the group, is that it is *easy* and *obvious* to sign up for recurring dues payments. Cash or other one-time methods should be seen as a band-aid, not a way to conduct regular operations. (And if you've got cash-only people, which I understand, offer a 12-for-10 program or something, because seriously, are they really gonna miss 0 payments during a year? Paying a bunch of months in advance is less overhead for everyone.) 
One thing we've never adequately pursued, I feel, is the notion of a $5/mo or $10/mo "supporter" level, where people get the warm-fuzzy of being able to call themselves supporting members or something (terminology gets tricky), but which is *only* available as a recurring commitment. We currently have 638 people signed up for the i3detroit-public discussion group, so if even just a small fraction of them signed on as supporters, it would bring in a substantial chunk of change, basically forever. They'd get to brag about the thing they're contributing to (loyal supporters from afar, remember?), and I'd happily teach 'em all how to cut their own hackerspace bumper stickers or something to further extend their pride and reach. 
Workshops and classes, in my experience, can bring in enough cash to cover their own expenses and maybe buy the instructor breakfast. But running enough of those and charging enough to cover the rent, would turn the group into a full-time school, and I don't personally like that. (My feeling is that we exist for people to DIY, not to be spoon-fed in a classroom environment.) Others may see it differently, but it's still very difficult to make the numbers work. Dues, dues, dues. Recurring dues.
-Nate B-(another one of i3detroit's founding members)
Edward L Platt  wrote:
>                 Without the details, it's tough to make a specific recommendation. In general, if dues and workshops aren't paying your expenses, you probably need to change something about your dues structure and/or spending. I wouldn't recommend trying to cover ongoing expenses with grants, it's not as sustainable.
> In the early days of i3 Detroit, we were having trouble covering our expenses. A few of us got together to figure out how to solve the problem (call it a committee if you'd like). We found that our expenses were low, but we just weren't brining enough money in to cover them. We had a lot of interest from potential members, but it wasn't translating into paid memberships. The two recurring themes we heard were "I just want a place to work on my crafts, or sit and code. I can't justify paying for access to large machine tools." and "I live far away and can only make it out a few times per month. I can't justify paying for 24/7 access."
> 
> Because there was interest and we had unused capacity, we chose to *lower* dues to bring in more members. Specifically we went from a $100/mo flat rate to $89 for full voting members, and $39 for crafter/coders or starving hackers (honor system). We almost immediately doubled our membership and haven't had trouble meeting our expenses since, even after moving to a larger space. About a year ago, we switch back to a flat rate at $49 to simplify things for the treasurer, and that seems to be working well.
> Happy hacking,-Ed
> On Sun, Dec 7, 2014 at 1:23 PM, Joshua Pritt <ramgarden@gmail.com> wrote:
> > You can do a pig roast bbq tech expo type event. $5 for a plate and all you can eat. You have each member bring something like plates, cups, food, etc. And while people eat you can show all the projects everyone works on. If you advertise it enough like on the local public radio and put up attention getting flyers with bright graphics all over town you could bring in a few hundred dollars. 
On Dec 7, 2014 12:10 PM, "Florencia Edwards" <floev22@gmail.com> wrote:
> > What do you do in day to day activities to earn money for the hackerspace? We have memberships and workshops but its not enough to maintain it. We are in crisis. Do you sell electronic kits, our kits you make there? Any idea is good. Thanks

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Edward L. Platthttp://elplatt.comhttp://civic.mit.edu/users/elplatthttp://i3detroit.com@elplatt
This electronic mail message was sent from my desktop personal computer.  Please forgive any long-winded, overly-prosaic ramblings.                