[Montego]

that picture is one of the rollers not the tensioner, the tensioner is a small hydrolic device which pushes against one of the rollers to keep the belt taught. the prices you have been quoted l doubt would include the water pump, you need to ask more questions about what you are getting for your money. what's your current mileage?
this is not an easy timing belt to change, make certain that whoever does the job knows what they are doing