You'll probably need (3) 5G pails from NYFS. Order directly from them, cost per 5G pail I remember being $150-160 each. Shipping was reasonable too. Very friendly and helpful folks at NYFS.
As a first year pro haunt this past season we built our attraction from scratch. Ordered roughly 200 sheets of ply wood that needed to be fire treated.
We ordered (4) 5G pails of FR and used just about every drop. Attraction was apx. 2700 sq ft.
Hop on the NYFS website it lists a lot of helpful info as far as how much product coverage depending on what you're treating.
If you're trying to figure out your sq. footage and how much FR you'll need don't forget to take into account each piece of plywood has TWO SIDES that need to be treated!
Hope this gives you better direction. I'd definitely say you'll need the best part of (3) 5G pails though.