TPS gone bad?

I will try to be as detailed as possbile.

I have a 2000 Focus SE 5-speed 100% stock. The check engine light has been on for a long time so I had it scanned. The guy at the shop told me it meant that the TPS is off. Sometimes the car will almost die, or die when coming to a stop. Every once in a while the rpms will stick when shifting too.

I hope this sounds like a problem that deals with the throttle body. How can I fix this? Do I need a whole new TB, or just the sensor, and where can I get one for cheap?

Thanks in advance for the help.