If you don't mind, I will convert your post for the benefits of users of the metric system. And while I am at it, I'll give the prices in uros as well.
SPACE: 25.6 m x 3 m of wall space total.
COST: I have to cover space, extra lights chairs and the like. I will come up with a formula of a percent of sales plus a figure for every 60cm of 3m high wall space. It will be very reasonable. If you really can't afford it and the work is fabulous, then we could work out something for you. If more folk participate, the costs plunge. I estimate the following plus 30% of sales to cover costs of sales assistants.
60cm wide 276 ($300)
90cm wide 414 ($450)
1.2m wide 515 ($560)
1.5m wide 653 ($710)
1.8m wide 818 ($890)
2.4 wide 1232 ($1340)
3m wide 1407 ($1530)
EXPECTED PROFIT: Last year about 70 photographers bought space at ~ 3200 ($3500) or more for 2.4m wide, 3m high (and it would cost only 1232 for us).
PRICING: The average range in general at this show would be from 180280 ($200/350) to 32004200 ($3500/4500) going from A4 / 20x25cm all the way to say 1.4m to 1.8m high.
I'll add an example of pricing for A3  12 x 18" prints:
For 3 prints, 4 prints maybe, we need 60cm (2 feet) of wall space (one needs a bit of space around each picture and we can't really use the bottom and top parts), so 276 / 300$ of wall space. Price per picture would be 280550 ($350600), of which you get ~70%, so 196385 ($245420).
