They have never followed the Blue Book Values. Supply and Demand.. If someone has a nice low mileage E28 M5, it will be in the $15,900 neighborhood, whereas some poor examples will sell in the $3000 neighborhood. I paid $11,500 for my 167,000 mile example. Car was immaculate with the ENTIRE service history. Previous owner was a fanatic and took great care of it. Without spending time with the previous owner and going over all the service records, It would have been an $8000 car.. The fact that REDLINE BMW in Pompano Beach, FL worked on it for most of it's life also contributed to a higher asking price.. So you see, many variables come into play with the value of the E28 M5.. Now the E28 M535i is something entirely different.. It isn't in any Blue Book... :)