backup light does not work. Bulbs and fuse are good.

What is your question?

My car is 2001 Toyota Corolla, Auto transmission. At first, One backup light did not work. I changed the bulb; but the light still did not work. After about one year, both light did not work. I change both bulbs yesterday. They did not work. I checked fuse and the fuse was good. Can you please tell me if you know the problem? How much will it cost if I had it repaired? Thank you very much, (my email: davidsmithd@yahoo.com) David