Eggcrate

Where do you buy your eggcrate at? I need some to make my frag grow out area as well as my skimmer lift to get it at the right height when my sump is filled. I've found it on amazon but it seems pretty expensive - are there any local stores that you buy it at? I've looked at home depot and can't find it, and I think I looked at Lowes and Menards too... can't find it anyplace...