This an easy swap. You need the shifter, cantilever compatible brake levers, 25.4mm clamp stem, a flat bar, cables & casings, a Shimano R443 ft derailleur and grips. You should be able to get everything for approx $200. If you sell your old parts you could recover at least half of that. Here is a link to the shifter:
http://www.nashbar.com/profile.cfm?c...s%20%2D%20Road to get you started. The hardest part to find will be the cantilever brake levers. They pull the same amount of cable as a road lever. Try Tektro levers. Good luck and post pics when it's done.
Tim