Well, you can get those flimsy-looking Sigma computers, I think you can pick one up for like $20 or something. Never had one but they looked pretty good deals or whatnot.

I'd stick with Cateye, though. You can get an Astrale with cadence for $35 easily and those things will last forever. Can't beat em.

edit: wow. posted at the same time as the other two guys and mentioned the same exact computers. freaky.