someone upthread recommended starting with Mark Waid's run, aka Volume 3, which was an excellent starting point for me. It doesn't assume any previous knowledge and repeatedly explains how Matt's powers work, and is generally an absolute delight.

If you want them really, really cheap *cough* go here: hcward.tumblr.com/post/118343806827 (and google comicrack for a good, free programme to read them on.)