I would: 1) determine the average yearly depreciation, then interpolate the price down the unquoted years, 2) disregard the sound system as
added value, 3) search for prices of similar vehicles on Craigslist or other classifieds, 4) ask what components have been replaced and when (the more the better, the less you would have to worry about replacing$$) if you are a shrewed bargainer this info ...