I went a bit overboard with purchasing cars (offline) but here's what I ended up with... lol
'96 Ferrari F50 GT (This car is a beast!)
'57 Ferrari 250 California
'07 Alfa Romeo 8C Competizione
'99 Shelby Series 1 (A600 upgrades complete)
'02 Chevrolet Corvette Z06 (S700 upgrades complete)
'09 Lotus 2-Eleven (R3/800 upgrades complete)
'06 Lotus Exige Cup 240
'11 RUF Rt 12 R
You had a very good day!
I've been gunning for that Ferrari Collector achievement, so off to the Auction House I went: -
[A600] F430 - 20000
[C425] 365GTB/4 - 96000
[S700] 599GTO - 165500
[S700] F50 - 253000
[R3800] #89 F430GT - ~596000
Thanks. That's what I get for being forced to watch my brother endlessly scour the market on FIFA 12 UT. The 599GTO/F430GT weren't buyouts either.
And as of this post, I can add a [B500] Dino for ~13000. Unfortunately, the only cars left are 1000000+, whose auctions are either already over the list price, or start stupidly low and end up over the list price anyway.
You should try getting together with some extremely trustworthy friends to attain the Ferrari collector achievement. A few buddies of mine and I got together and split the collection of cars evenly. This saved us a lot of time and in-game credits. I'm pretty sure the auction house market is different now but everyone was able to sell the cars they didn't want to keep, for profit in the auction house.