I haven't tried that, but I did try photographing my slides on a light box with a digicam. The results were not too bad--the limiting factor seemed to be that I couldn't get my camera to focus close enough to the slide to get the resolution I wanted.

There are services that will do bulk slide scans for cheap (under a dollar each), but even that could run into a lot of money for a large number of scans. Doing it yourself could take a lot of time, though, if you really want to scan them all.