Already there! At 1018 unique cars now, got all the premiums, and am left with 20 standards. My car list is in my signature.
Got most of my cars myself "legit-ly", except for those 67's cars (through the birthday glitch) and a number of the race cars (from trading online). However, I did create a few sub account to earn extra money from the seasonal events. Not sure if that's cheating, it is debatable.
All in all, it is a rather hard journey with quite a bit of farming, but nothing beats that trophy ding when I reach 1000 cars.