Thermostat Change Cost on 1999 Chevrolet Metro

I was in a accident that caused my engine to overheat, and stall. I took it to the shop and they informed me that they would need to change the thermostat in order to see if there is any internal damage to the engine. I understand this process, but was told it would cost around $305 to do so. According to, it would only cost around $120 at most. I am trying to see if there is a reason for the large difference in cost. Whether it has to do with them doing more tests, or they are just trying to rip me off.

Asked by for the 1999 Chevrolet Metro
They might have a diagnostic fee included in the price, But repairpal's estimator is right on the money as my book shows .8 of a hour and about $20 for the themostat
Yes as it states on Repairpal's estimator the prices don't include diagnostic fees
I believe diagnostic tests are going to be conducted after the thermostat is changed. Would that justify the high cost?