Syrpentine belt tension problems

[fsusurfer]

Hi folks, this is my first time posting here and I wanted to ask for some advice. I have a 99 GT 'vert. Recently I hard a squeaking noise coming from what seems to be the serpentine belt. Took it to the shop. They said I have a belt tensioner problem. Said the charge would be 185 for new belt, tensioner and installation. Anyone had this problem before...suggestions? Thanks for your help!