Toyota Repair: Brakes, warning signs, rears

Question
2001 Camry Approx 40,000 miles
What is the average amount of miles when you should have your brakes repaired?  Also, what are some of the warning signs?  Whats is the  average cost of brake repair?  

Answer
Deapends on driving habits and Local Vs Highway.
seen them go at 15K and last 100K
Have them checked every other oil change.
Front brakes are $99 -$399 depends if you need new rotors.
Rears about the same.
Dont know if you have rear drum or disc, you didnt say.

Mike