Where can I get information on used car sales on a state to state
basis listing make model milage and selling price for the purpose of
comparison with other states (as in buy low and sell high)

Hi! Thanks for the question.

I included those sites that can search by state directly and not by
zip code since I imagine that it would be such a tedious exercise on
your part. Here is a list of sites that you can go to. I also included
only those that filter the results based on the depth you require.

Yahoo Autos
http://autos.yahoo.com/usedcars/search/revise/revise.html?make=BMW&model=318I&cl_y=&ch_y=&cl_price=&ch_price=&cl_mi=50000&ch_mi=75000&ck=&gur=50&csz=California&ce_sl=&vtype=autos&mk=BMW&mo=318i&submit=Search&r=1&sr=0

New York Times Auto Search
http://autos.nytimes.com/autos/search/ 

Cars.com (Only has a specified number of city states but may still be
helpful for comparison purposes since the popular locations are found
here)
http://www.cars.com/go/search/advanced_search.jsp?tracktype=usedcc&aff=thestate 

Domestic Auto Sale
http://www.domesticsale.com/autoclassified/

AutoNet USA
http://www.autonetusa.com/carfinder/ 

2Buy Cars
http://www.2buycars.net/services.htm 

AutoBase
http://www.autobase.com/cgi/list.exe?newsite=1 


Search terms used:
nationwide used cars autos state classifieds 

I hope this would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if
you would need further information.
                                                          
                              
Regards,                              
Easterangel-ga                              
Google Answers Researcher