Hi,
I believe what you are looking for is The arimax method (which is the same as arima but with independent variables).
I would recommend inquiring each series separately so you can look at the structure of each series (unless you are looking for the average price of all car models.).
BTW: why not using the difference between each time period ? (T2/T1-1)
I SUGGEST YOU GOOGLE ABOUT ARIMAX.
about AUTOREG - it is a simplier form of arima (AUTOREGRESSION-INTEGRATED-MOVING_AVERAGE)
hope this helps.
keep posting