I bought a Sterilite 1960 rack from Animal Plastics, but only got a 3-shelf one. I need another to house more adults but don't want to drop the kind of cash it takes to buy one.

I want to build a rack to the same specifications (obviously with more slots), but where can I get good materials? Lowe's has melamine shelving, but they're pre-cut and not wide enough. Is there a better material out there, more similar to the high-density PVC that AP uses? Where can I get it and how much would I roughly need to spend?