While most people visiting my website are looking for a database with car specifications and prices when new, several people asked me if I can provide used car valuation database.
United Kingdom car database made from personal interest sourcing data from Parkers.co.uk also contain min-max ranges of used cars currently listed for sale.
Other customers asked me for similar databases for United States and India. Indians suggested me to extract data from www.cars24.com/car-evaluation but this website is difficult, because I need to select Make, Model, Year, Fuel, Version, State, RTO number, KM driven (too many variables to make scraping feasible), then enter my phone number to get resulted value (and probably have my phone number sold to SMS marketing spammers).
The CORRECT way to make a car valuation service is to use a database with new car prices, another database that adjust price based on car age and/or miles driven, another database that adjust price based on state / ZIP code. I can provide you database with car prices as new (MSRP / showroom price), but not the rest.