As mirrorshard says, you don't have to stay in the con hotel, and you can buy a membership for just one day if you wish.

Membership has to be compulsory - although the con is run entirely by unpaid volunteers, we have to cover the non-trivial cost of running it. The curse of the conrunner - if you make a profit, it either goes to charity or the next convention. If you make a loss it comes out of your own pocket. (No laughing matter. I personally know three committees that made losses of varying amounts.)

Next year's Eastercon will probably be in Birmingham.