How much approximately would it cost to have an engine repaired off of a toyota MR2 that had been overheated. The motor will start but runs rough. I don't own the car but it is being sold for $650 and I want to know if it is worth buying. Serious answers only please.

This is hard to say, without knowing the actual damage, what has been repaired, if anything. Worst case scenario is an engine replacement that would cost about 400-700 dollars labor and about 500-1000 for the engine (if you get it from a wreckign yard.

if the engine is scrap then depending on the year it might be Worth it for the Rolling chassis