As a point of comparison, I had my M2 overhauled by a top repairman here in the U.S. recently. My curtains were fine, but if I had wanted them replaced he would have charged me $125 per curtain (so $250 total) plus an additional $160 over the other CLA costs I was already incurring -- because of the extra degree of dismantling required to replace the curtains. I have had my IIIa worked on but that was some time ago, and I'll admit that I'm not sure if a IIc is easier or harder to work on than an M-series camera (I would assume easier as I think you can drop the whole shutter mechanism out the bottom -- I could be wrong).
Perhaps you want to hold off on selling your M-Elmar 5cm f/3.5!