To obtain the Ferrari Collector achievement, you need to own all of the Ferrari's in the game that were included on disc 1. There are 22 total cars you will need. Here is the list of cars you will need to collect and their retail value. An easier way of obtaining the cars without paying the retail price is by looking on the auction house. You can get cars for literally a fraction of their retail price.

Car	Price
1957 250 California	[3 Million Credits]
1957 250 TR	[8 Million Credits]
1964 250 GTO	[10 Million Credits]
1967 330 P4	[9 Million Credits] (Free as a Level 30 Reward)
1968 365 GTB/4	[270,000 Credits] (Free as a Level 16 Reward)
1969 Dino 264 GT	[55,000 Credits]
1984 GTO	[320,000 Credits] (Free as a Level 25 Reward)
1987 F40	[380,000 Credits]
1991 512 TR	[75,000 Credits]
1995 F50	[400,000 Credits] (Free as a Level 31 Reward)
1998 #12 Risi F333	[2.2 Million Credits]
1999 360 Modena	[90,000 Credits]
2002 Enzo	[1.3 Million Credits]
2004 F430	[150,000 Credits] (Free as a Level 28 Reward)
2006 599 GTB Fiorano	[310,000 Credits]
2009 California	[220,000 Credits]
2010 #83 F430 GT	[1 Million Credits]
2010 #89 F430 GT	[1 Million Credits]
2010 458 Italia	[240,000 Credits] (Free as a Level 34 Reward)
2010 599xx	[1.5 Million Credits]
2011 FF	[280,000 Credits]
2011 599 GTO	[370,000 Credits] (Free as a Level 36 Reward)