We've discussed digitising your old photo negatives before, but dedicated negative scanners can be expensive. Photographer Claus Thiim, however, built his own using just a few toilet paper rolls and an old polariser filter.
If you've got stacks of film negatives in the basement that you want to digitise (even just as a backup plan), you don't need to spend a fortune to do so. By taping some toilet paper rolls together with a polariser filter on the end, you can "scan" your slides by photographing them through the filter with any DSLR camera. Just make sure you've got a good light source behind the film, and some high-quality photo editing software to make up for the lack of advanced hardware. It's certainly a cheap alternative, but for the purposes of backing up your photos, it's a good solution. Besides, if you haven't sprung for that scanner yet, it's certainly better than nothing. Hit the link for more details.