I did some temporary foaling stalls with the mini panels and zip tied plywood to them. I did others with plastic sign board zip tied to them these worked better they were easy to clean and they couldn't chew them the sign board was comparable price wise to the plywood.
The roof and your posts plays a big part in how you are going to build your stalls because its the roof that is going to have to shelter the plywood. .
How about you post pictures of what you have to work with and then we'll go from there.
The least expensive I've heard of is building walls with straw bales and driving rebar through them to keep them standing, then using tarp for the roof.
If you have access to pallets and plywood (or siding), you can build a pretty decent shed-roof run-in for very little money. The pallets serve as the framing, so this is built like a tank!
Here's the finished shed (This was built as a storage shed...I'd want to add windows or do without the doors).