Why bother asking us? Go down to your local Home Depot or lumber yard and see what sheet goods they have and what the prices are. Particle Board, MDF, Oriented-Strand Board (OSB), CDX plywood, just about anything can work... Heck, if you want super-cheap, build a frame out of some 2x4s, glue, and screws, then skin it with whatever 1/4" sheet good you can find. You'd probably need a small piece of 3/4" material for the control panel top. If you can wait a couple of weeks (or months) for the 2x4s to dry, you'll have better results.