I was thinking something similiar to what Jesse suggested. I remember at C3 that there was a separate hall for the "fan stuff" and I would have been surprised if it were the same costs as the booths in the main showrooms. I was going to suggest talking with someone from FFURG to see what their booth cost as I remember going there (in fact it was my first customizing experience
Having said all that, even if we get a booth for very low cost, I still think a fundraiser is a good idea. There are definitely material and shipping costs that we are going to rack up for this project. Although I've got no problems donating some time, materials, figures etc, its still going to be expensive.
One suggestion on the auction route... what if we put together a monthly group project to make a custom to auction off. Obviously, it may not be customs we would typically make or that we might get burnt out on (clones for many). If we get 10 people to participate we could raise $250-$500 on eBay. We'd probably want to stagger the auctions so that the market wasn't flooded all at once either. Anyway, just a thought.