norelec, here's an option:

• $20 Shimano HG-37 7-speed Hyperglide freewheel, 14-28 teeth
• $30 Shimano ST-EF28 (for V-brakes) or ST-EF20 (for cantilever) EZ-Fire Plus shift/brake lever set with new shift wires
• $15 Sachs PC-41 chain

Your present derailleur should work with this setup. If you don't have the tools and/or expertise to take the freewheel off and set up the brakes and derailleurs with the new controls, having your LBS do the work will probably run you $30 to $40 (where I come from, anyway). If you just needed them to pull the old freewheel so you can thread the new one on, that would probably set you back $5 or less.