This stuff seems to be pretty expensive in general. Here's a thread where I explored some options.
http://forum.arcadecontrols.com/index.php/topic,164617.0.htmlMine was for vents you wouldn't really see, so you will probably want to stick with the aluminum grill type material on the front. If you have a nice drill press and a lot of patience you could probably make your own for less. You could also look at thrift shops for old speakers and possibly get some material that way.