Try CPI- Value guide to cars of particular interest, luxury & high-line vehicles 800-972-5312. My copy was given to me when I purchased my car in 99'. It comes out every 3 months and lists a number of older collector cars. I have never subscribed, it is fun to look at the old one. It has its own Mercedes Benz SL model section. In April May June of 99' it shows a 63- 67 230SL as $22,800 and a 67-68 250SL as $20,000. I would be interested in what they show as a value today.