Thanks for the guidance. Here is what I decided to do for now. After showing my pictures at some reputable body shops, and getting guesstimates in the $5,000 and up range, I knew my options were "do a cheap hack repair" or "walk away", and I was really, really leaning towards walking away, because I just did not have the time or energy to do the work.
So I ultimately decided to look for a less spit-and-polish body shop... to find somebody else willing to do the hack repair instead of me. I knew that in the local classified paper were advertisements for shade tree mechnics like, "Head Gasket, any car $300, fixed or free".
With some reluctance I called one of the mobile body repair guys, to see if they were willing to work on transplanting parts from a donor car. So far -- with no work yet done -- the experience has been good. The guy met me at the yard where the car was. He was quite professional, asking a lot of detailed questions about what I wanted to do about the airbag and such, and filling out a real written estimate. I could tell he has done this a lot.
I asked about parts, and he told me that by using the "pick-your-part" type junkyards which offer flat rate pricing (any hood, $29, even a Mercedes hood... any fender, $27, even a Mercedes fender) instead of the premium dismanters that seem to price based on fraction-of-retail, he could get all used parts for way less then the donor car cost. He said the "pick-your-part" places were actually a good place for Mercedes in particular, since its a rare Mercedes owner who also wants to wrench parts off a wreck.
So for less than $750 parts and labor, he purports to give me my car back reassembled with junkyard parts, ready for painting. I decided to chance it. Included in the cost was him towing the car on a rented dolly to *his* garage -- he charged me only for gas and the dolly rental -- and he would have charged the same to tow it to my garage and do the work there. His doing the dolly tow saved me $250 in towing. I'll post again when the work is done. I know it will be a hack, but I figure his hack will be no better or worse than mine would, and he's doing basically all the parts chasing and wrenching I did not have any time to do.
The cost did not include the airbag, since at that time I was thinking of not doing it, but based on the earlier comments, I think I will call him and ask him to replace the airbag, too.
My justification was, "it will cost me $250 just to tow the wreck home, so for $500 more than that, I can *drive* the car home from this repair shop and even if the repair isn't pretty (and I don't think it will be), I can at least have the car home safe while I sort out what to do.
Stay tuned for the exciting conclusion.