IF this has happened to the car, figure in the price of another engine as valves are not the only thing damaged i'll bet!! They hit the pistons when the engine gets out of time.
Why else would it be for sale? Now, if it is a nice car otherwise and you can get it at a steal ok. Could run 2,500.00 + depending on what has got to be done, no way to tell without a tear down of the engine! Then you owe for that also even if that's all that is done. Transmission, steering rack and suspension 'supposed' to be in good shape?? No way to tell! IF it were ME, I'd pass!!!