As detailed on Bizarre's official site, the content will hit the online Xbox Live Marketplace on February 14. It will arrive in both free and premium offerings, with the latter priced at 400 Microsoft Points ($5). nope
The Free Challenge Pack contains two new game modes, a new car, and seven new achievements. On the other hand, the Premium Challenge Pack has everything contained within the free pack plus another gameplay mode, six additional cars, three new bikes, and three more achievements.
Both packs will add the TV Camera cheat as well, allowing players to race from the perspective of the replay cameras. For more on the content, including specifics on the vehicles and gameplay modes, scope out the full details.