I've seen absolute parts cars sell for $20,000 in the past 6 months (end buyer had no intention of restoring, as end buyer was a Mercedes dismantler / parts outlet).... cars like the really rough one pictured above.
Have you looked to see what parts are going for these days? The chrome strips on the doors of a 230SL cost just as much as those for a 280... as they're identical... in the UK I just saw a price of 220 GBP, the Classic Center charges about the same (just priced a complete set, for both sides of the car at $800). How about the little latches to secure your 230SL hard top... $550 a pair at one place I found. God forbid you need body panels... putting in a new trunk floor? You might as well Papier-mâché your trunk with $100 bills.
I only see the prices of all Pagodas going up as parts prices increase, restoration costs increase, etc. etc. Any restorer will tell you, it's cheaper to buy a well restored car than a basket case and try to oversee a restoration yourself. Unless that's what you like doing, and for a lot of people, that's their thing... but more often than not, people end up spending $125,000 and end up with the nicest $85,000 250SL. It depends what you want. Buy a less than perfect driver to drive and enjoy... that's what I did.... if I want a better car, I'll sell the one I've got and buy a nicer car because trying to make mine into that 'nicer' car will take more time and money than I'm interested in spending, all while having nothing to drive for the what, year, year and a half (easy) it might take to have the car restored?
I always say... "There is nothing more expensive than a cheap Mercedes-Benz".
