It's not a Contax III, but a Contax IIIa. Serial number put it made between October and December 1954. There were 5 000 of the "C" series made in late 54, early 55, so not exactly a rare item, this out of the nearly 70 000 Contax IIIa made between 1951 and 1962. This one has the more common "color dials", not as rare as the early "black dials". This also affects value.
This is obviously is wonderful cosmetic condition, but value will also depend on who your friend wants to sell it to. A collector who would want to keep it on a shelf might pay higher than someone who actually wants to use it. In that case, value will depend on whether or not it's in good working condition.
Like any mechanical object, a camera actually needs to be used to be kept in good working condition — used often, and cleaned, lubricated and adjusted often. If it's been sitting on a shelf or in a box for the last 60, 70 years, chances are it'll have problems. Moreover, Contax IIa and IIIa have known problems that develop with age, notably to the shutter and the viewfinder—I just had to return a IIa to a seller because there was major vertical alignment problems in the viewfinder, something that often happens with this camera. Lots of info on this here:
http://zeisscamera.com/first.shtml
People buy old film cameras less and less for collecting purposes but more and more to actually use them—this is the case even with Leica cameras. A perfectly working camera with esthetic defects can be as much, if not more valuable than a non-working beautifully kept camera. Before asserting value on this one, that needs to be checked.
Lenses will need to be checked for the usual suspects (dust, fog, fungus). The 50mm f/2 Sonnar is not as valuable as the 50mm f/1.5 and sells for about 175-200$US on eBay these days. The 35mm f/2.8 Biogon is supposed to be a great lens. You can find one for about 450-500$US. Again, precise value will be determined on the working condition of the lens.