Many of the older low-count spoke wheels made by Shimano are availabe on the cheap since the first upgrade most people make is the wheelset. CanadianCyclist.com has a good classifieds section for that sort of thing, I picked up a set for $100 with rubber last year.

edit: if the hubs are also Shimano 600, you might want to keep those wheels as they are, they are amazing hubs IMHO. I've got a set on my beater and they are very very smooth and fast, I love them.