I believe that many bodies were sold for $50 back in the 1950's and I can tell you that many were moved/traded, etc over the years, and still for cheap in many cases. One guy I talked to got his NG car body in the 1980's for...$25...a heck of a lot cheaper than a storage shed.
Floyd Reed, who scrapped many of the D&RG cars must have sold quite a few (We know that he got 6 of the 5900's and 4 of them turned up on farms), the D&RGW sold some, as well as the scrapping firm that got much of the equipment at the end of NG operations. And as Dave mentioned, up around Montrose, many of the cars, particulary stock cars, were sold in 1953, although I believe that a scheduled auction didn't take place. I think people just came forward with cash.
The RGS also sold some of their cars, though not many. One of the Miller boxes turned up on a farm near Olathe a few years back.
To give you a rough idea, at least 1/3 of all of the 3000 series cars still exist. Over 150 of these are carbodies, and of course, more probably did exist but have been lost to neglect or fire or cut up for firewood. My Dad and I didn't even try to count all of the SG cars, but my best guess is that there are probably 500 or more SG cars in the San Luis Valley, as they were more common.