is your 7 speed a cassette or a thread-on free hub?
I just bought a new rear from my LBS, nothing fancy... 26" 36 spoke with quick release skewer, it was $65, included rim tape if that counts for anything.
jensonusa.com has (had?) one for $35, front or rear. certainly cant expect anything to be of the utmost quality at that price but for some mild riding, how bad can it be?
(edit: here is the link for the $35 wheel...)
http://www.jensonusa.com/store/produ...tb+Wheels.aspx
another edit: those rear rims are for cassette hubs, i dont suppose that matters much if you can find a 7 speed cassette of your liking... not sure how easy it is to switch between 7 and 8 without adjusting your derailler but thats another option, if it doesnt require any adjustments, you can get a decent 8 speed for ~30 bucks.