The early bird gets the worm they say, well in this case you can get that metaphorical worm for only $4 with the Forza Horizon 2 Pre-Order Car pack. Until now you could only get the pack of four cars if you had pre-ordered the game but now you can simply purchase it.
The pre order car pack includes the 2011 Lamborghini Gallardo LP-570-4 Superleggera with a full carbon fiber interior, the 2013 BMW M6 Coupe with 560 horsepower coming through a twin-turbo v8 engine, the 2008 Ferrari California that gets up to 62 mph in under 4 seconds, and the 2013 Audi RS 4 Avant which they state can hold its own against anything "short of a supercar." The announcement and full car breakdown can be found in an Xbox.com post about the pack’s availability.
There are plenty of Forza Horizon car packs to meet your fancy including Fast and Furious, Top Gear, Alpinestars, and more. Having packs like these helps games remain fresh and also adds a level of personalization to the game. $4 is a relatively small price to pay for downloadable content, though if you want to have every single car available the total price could climb quite a bit.