If you want pallisade fort walls, they're relatively easy to put together for rather little.
Get some of the smaller craft dowels that you can get in a package at the craft isle of walmart type stores, the small craft sticks, and the wider tongue depressor type ones. Use the wide ones as a base, cut the dowels in thirds and line them up using the craft sticks to reinforce them a bit. Add a bit of basing to the bottom, and they work rather well.