The question in my opinion involves not only the cost of engine renewal, but the remaining service life of other major components:

How many miles on the transmission? Rear Axle/Differential? Power Steering Pump? Radiator? Climate Control System? Struts? How much downtime can you tolerate while the items are repaired/replaced as they fail?

I guess what I'm saying is that while having a sound bodyshell is a major plus, it's possible that other i$$ues are on the horizon. I would wonder if investment in an early-Nineties 190 with about half the mileage would be more prudent. I think blue book on a 1993 falls under $10k.