Yep, what SteelHeadz said. My '03 just recently started sounding like a small pig in duress but I'm going to lose the belt tensioner during my York OBA install anyway.
Places like RockAuto.com carry these from various manufactures running anywhere from $42.00 (for the one pictured) all the way to $62.00. I believe the FSM recommends changing these along with the serpentine belt which you should have already done or are certainly due for one considering the age of your rig.