"Original" Behr unit for 3.5 coupe was just sold on E-bay in a few hours. I saw it for the first time ever there. Check this link:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=4549090835&sspagename=STRK%3AMEWA%3AIT
At Silver Star Motors(?) I was quoted $4200 for the whole system. I would like to have original unit, but this price is half what I paid for the car. I just bought Kuhlemeister unit for $300 and going to put it in. These were used till 1968 in w111 cars. I think this is the best choise for the money. But this is only one component of the A/C system. Don't forget about compressor, condenser, drier, hoses, wiring...
Vilius