It is safe to say that prices on 91s have gone up in the last year but not 10K. Then again, the only thing you could get even three years ago for 20K was a beater with a salvage title or, from a desperate used car dealer, something in so-so condition with a ton of miles on it and needs. Average for 91s sold on Prime in the spring of 2014 was around 29-30. This spring the average seems to be running around 33. This is pretty much in line with condition 3 valuations on the Hagerty valuation web site. But as arista pointed out, prices can vary wildly depending on condition and mileage. You might still find a high mileage salvage title in decent shape in the mid 20s while a pristine example with mileage in the teens, full service history, and no service needs could go for close to 60K.