Here is my story with restoring a W111 coupe.
I always dreamed of having a W111 cabriolet 3.5. By the time I could make the dream come true the prices went so high that I had to settle for a 250SE coupe. I found one close by in NH that had a partial restoration in 1990 and never touched since. It was painted in the original anthracite grey and had a new/rebuilt 230 engine transmission. My initial plan was to eventually transform it from a 111.021 to a 111.027 (I know, crazy).
Attached are 2 pictures from when I brought it home 09/2013 and 2 pictures from yesterday. It appears that all I did was to put chrome back on. And yet since then I worked on it almost all afternoons and weekends to the point of very pissed off wife. And I am not done yet, I still need to get correct leather interior and solve an annoying rocker noise.
I worked on: fuel tank (twice), fuel pump (still working on it), fuel lines, IP valves, IP adjustments, injectors, CSV, all other throttle adjustments, all of the electrical, temperature sender, fuel sender, all filters, wipers mechanism, heater core linkages, radio, instruments, horns, steering, suspension, springs (all, PITA), rear axle, all rubbers and it goes on and on.
I used to be frustrated with the high restored prices but now I know why. I consider myself lucky to have a solid engine and IP and no rust. I am getting attached to the coupe look so I may abandon the idea of making it convertible. I had it professionally polished and it looks so good that I will keep it grey.
As other people mentioned here rust and sheet metal work is the most serious factor, it is very time consuming. I know how to weld and I have welding equipment and yet I avoided anything that had rust.
From your posts it appears that you are not looking to do it yourself. If you do decide to part it out send me a PM and I will be there next day for parts. If you do decide to restore it I will be happy to help you through it.