Wow, I'm sure you could get at least 10 local people to share the cost of that and they'd be thrilled to have ALL that room to spread out.
Are tables/chairs included in the rental?
What about electrical outlets?
Enough not blow the box?
Make sure someone brings a bunch of extension cords.
Oh, make it a phone-free zone.
I'd gladly pay the money to not have any distractions and a lot of room to work.
Everyone could do their own thing, and potluck lunch is fine.
You could charge a bit more and have it included lunch - just get the local deli to make a few platters and bring drinks.
Wow again. 3 days, 9AM-10PM just. to. sew.
Heaven.