The pic of the tensioner looks correct. $50 for any quality tensioner is a good price. The idler pulley can be checked for bearing smoothness and any noise. It's not a bad idea to change them both to eliminate trouble down the road. $50 labor is not bad considering all the overhead to run the shop. Probably 20 - 30 minute pay rate.

James

PS it is not uncommon for a shop to charge $100/hr when you supply your own parts.