The outcome of a local repair shop rebuilding the alternator is really dependent on the problem. If the basic windings are sound, a local guy can repair all the rest of the mechanical and electrical items displaying signs of wear. I doubt a local guy would actually rewind the machine as these things are done on purpose built machines that are not normally part of a local repair shop's typical set of equipment. So, they would send it out for that. By that time the bill would dwarf the cost of a new unit from the dealer.

My local guy (Groton Auto Electric, in Groton, CT), who I haven't used in quite some time, would do some tests to check the windings and if they were weak, he would tell me he recommended a rebuilt unit from Bosch which he would gladly supply at about the dealer pricing. If the windings were ok, he would go ahead with the repair, which involves new bearings, turning the commutator bars down to be concentric with the bearings and smooth, replacing the diode wheel, and cleaning and repainting the body/frame. He ran a test afterward at rated current and voltage for long enough to get the unit too hot to touch, and then megger checked the windings again, hot. If all was ok, I got the unit back. In the old days he would do this in an afternoon for me and charge about $65 to $95, depending on the alternator and what really needed to be done. I have no idea if he is still in business or what his prices might be today.

I think these kinds of shops used to be all over, but maybe the cheap rebuilds are putting them out of business.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)