With the problems, I'd offer scrap value ( $ 200 to 300 ). Mechanical parts can be changed so working with a no rust car carries high value.

Why does it need head gasket replaced? If for an oil leak, the front cover between the valve cover and block tends to leak but can be resealed. My 97 C280 with the same motor has a crank seal that needs replaced at some point.

You'd be missing out on a great inline 6 / electronic shift trans combo if you pass on this car. ( or any other car that uses the M104 and 722.6 )