I agree, the belt from NAPA around here is about $33, but the Tensioner is just over $75.
Are you capable of doing the work your self?
If so I would put a new belt on and see if it is still squeaking. If it is then i would put the tensioner on it.
If I had to pay for it to be done I would just do them both at the same time, it will save on labor cost.
07 Sport/Entertainment, Factory Hitch, and more to come!