A friend collected 'RS's to the point he had every model, every year of all the twin shocks. All were pristine, low milage, collectible. I believe at one point he had 20+. I believe he's one of the most knowledgable about these bikes. He decided to sell off his bikes and now only has three, a '77 with 8k, a '78 Motorsport with similar milage, and a '79, same milage. I looked at the bikes a month and a half ago. All had been sitting for awhile. The silver RS had both the solo and dual seat. He said he'd let it go for $8,5000. I believe that's a very solid price. He could advertise and easily get more. It is low milage and pristen but also has been sitting for a few years.
A RS is a unique BMW, considered one of the more special bikes ever produced by many motorcycle enthusiasts. In all seriousness to offer $3,000 is an insult to your friend - unless there is serious damage that the picture didn't show or that you failed to mention.
These bikes are very valuable to many. That's not to say they are that valuable to all. The early model 'RS has moved from a older motorcycle to a collectible motorcycle. That's also true of many airhead models whose current market value has risen quite a bit in the last five years. When any object becomes collectible its value becomes almost totally subjective.