Phenolic sheet can be had from Mcmaster Carr for $65 ish +shipping. Aluminum can be had from online metals for $30 ish plus shipping. Both would require a trip to a machine shop. Better yet, if you have an iron monger local, a drop piece of .5" aluminum would be next to nothing. That route would also lead you to a machine shop. With careful measuring, and the correct bit, you could do it yourself.