1995 Acura Legend overheating problems

Engine Cooling problem
1995 Acura Legend Two Wheel Drive Automatic

My car was overheating and the radiator was replaced.
Overheating continued and the radiator was replaced again (under warranty) and I paid $550.00 for the labor to replace the radiator.
20 minutes after this repair (2nd radiator) the heater hose blew and the mechanic fixed that at no charge (orginally told me it was going to be $150)
Now, my car is still overheating and the mechanic says it is the head gasget. He said that it is cheaper to replace the engine with a used engine. I do not have the price quote for the used engine yet. He told me that the problem was the radiator and that $550 will fix the problem. Initially, I told him that I was considering purchasing another car if the repairs were more than $500. Are there not diagnostics to pin point the areas that need repair in this case? In other words, I feel like I am getting ripped off.