You have to buy a car that's worth at least 1.000.000 Cr.
Smartest thing to do would be to amass 10.000.000 Cr. for
Then just buy the "Formula Gran Turismo" in the Online Collector's Dealership for 5.000.000 Cr. (you'll need it in a later championship) and grab both
at the same time.UPDATE: As of today, 31st May 2014, the online part of Gran Turismo 5 is no longer available. This includes the Online Collector's Dealership. You can still find the "Formula Gran Turismo" in the normal Used Car Dealership but you might have to wait for a while for it to appear here.