I bought my '95 G320 from Norm a few months ago. He has a pretty good inventory and very fair prices. Like any used car be sure to view it in person. We all have unique perspectives on condition. He has a website at
http://www.keisermotors.com
Which model to buy? How much do you want to spend? They run from $15k-150K. The early Gs are reffered to as the 460 chassis ('79-'86 in the US) and the newer versions are 463 chassis ('90-Present). 460s run $15-25k and 463s from $40k on up to the stratoshpere. The 460s were offered with several powerplants. They came as 240 and 300 diesels, no turbos. The gas engines were the 2.3 4cyl 230 and the M110 2.8L 6cyl arguably the best choice in a vehicle this heavy. The 460s ahve a very basic interior, reminds me of an old Isuzu Trooper. They are equipped with a part time 4wd system. 463s step up to a modern MB sedan style interior availible with all of the amenities. They also get an updated full time 4wd transfer case. Engines availible are the M103 3L six from '90-'94, the 350 diesel (problematic) and the M104 3.2L six from mid '94-98. After '98 the 5L V8 from the new S class is the power plant.
Other than Keiser Motors I know of a 300GD auto SWB in pretty good shape for ~$10k for sale privately in Minneapolis. Brent