I found a good deal on JensonUSA , for some wheelsets, only for disc brakes for $145, the Sun ringle/ single track. I know its out of your budget. But I also found some "disposable" brakes. They were like 19 bucks, by Tektro. Those will work until you get some more money in your pocket if you can't wait and save. I am going through the same thing you are. V-brakes just don't cut it.
http://www.jensonusa.com/store/produ...+Wheelset.aspx

http://www.jensonusa.com/store/produ...isc+Brake.aspx

Later,

Another MTBiker