Depends how patient you are. I don't think anyone sells it in pots, it's just clumps. It's actually really fast growing so you could easily propagate enough from one portion.
If you want to cover the whole area in one go, then I'm afraid I can't help - need to know how much a clump is, and what you're going to tie it to. Err on the side of caution and order less than you think if you're unsure - it'll fill in in no time.