FYI: I just installed new radiator today in my 82 SD. The wholesale cost on the non aluminum radiator that was recommended was $138.00.

Sit down with the mechanic and tell him your concerns, let him know up front that you will abide by his decision as to what is fair. Tell him you have appreciated all he has done, but you aren't excited about the added expense that could have been possibly avoided. Put the bee on him to tell you how he would expect to be treated if he were you.

If he gives you a reduction, he has proven his integrity and you should keep him. If he doesn't, attack him immediately or just don't use him again, whatever meets your needs.