Fixed by Microsoft before? If it's been opened up by someone else then the warranty seal has probably been broke. But if it hasn't then check the manufacture date on the back and if it's within three years then you can just sort things out via the MS website.
But yeah, dunno how much the guy charges. He posts a lot on Maxconsole, which is how I found him. Won't link you to his profile there as I imagine you need an account to view the details, but he's the
OP on this thread - his contact details are in his sig.