You know those things that you put under florescent lights? Like those plastic flexy sheets? Well, the back of them is super smooth. They are like $2 a sheet. But a few of those. They will chip alot, but I had it last for the whole season before i had to replace it.
To cut them to size, you can either cut them carefully with a saw, or you can etch the plastic and break it. Use pvc for coping that is just a little bit above the plastic. Use caulk for wood to hold the plastic on. As long as you aren't distastering from really high it will work, and it's cheap.