If you can find something used thats a good way to go, but if youre out of luck and need something new I agree with Kai. Eggcrate is great because its cheap, and open so water flows through it with not much restriction. I have owned the dividers you can buy at a lfs and they are flimsy and restrictive in terms of water flow. Egg crate can be cut to any size, you just need a good set of cutters and its pretty easy. Either way good luck with your search.