My brake light is out.....tried replacing the bulb but had not luck...am i missing something or am i having an electrical problem?

PS - Other than the brake light, my tail light is fully functional.

 

Your harness is shot. You're gonna' need a new one. Common issue.

 

Is it expensive? DIY job?

 

might just be a bad connection in the socket
check the metal tabs that the bulbs touches. mine used to do that and when i moved the bulb around it would work. i had to bend the tabs out more and it fixed it

 

It's pretty darn easy. All you do is slide out the old harness and slide in the new one and pop all the bulbs into the new one's sockets. You can also try and see if jiggling the bulb does anything. If that works, then you may need to take Soonerfan's advice.