iFixit has a
replacement guide for the top case. Also, google for "macbook_13in.pdf" should lead you to a PDF of Apple's service manual. Apple's has a lot more info about the different screw lengths, which is helpful (there are probably 15 screws to remove, all small and different sizes).
The top case is one piece and includes the keyboard, trackpad, and power button. It all goes through one ribbon cable and small connector. I would take off the top case, and see if the connector or board is sticky. You'll be able to see the rest of the logic board also, in case something else shorted.
There were four different top case parts used on the 13" MacBooks--white and black with dashboard/expose/play/pause keys, and white and black without the extra keys. Going price seems to be around $120-150.
PBParts seems to have good prices, iFixit's prices seem higher. And I didn't look, but I'm sure these things are on eBay too.