Sometime this week, Rockstar is to release a trailer and website section for the Midnight Club: Los Angeles's DLC. However, it seems Business Wire published the press release a bit to early. Today, Trading Markets posted the press release which reveals that the paid DLC pack "Premium Upgrade" will feature:

• Nine new vehicles:
      Luxury: 2008 Mercedes-Benz CLK63 AMG "Black"
      SUV: 2008 Range Rover Supercharged, 2008 Range Rover Sport Super Charged
      Lowrider: 1955 Chevy Bel Air, 1963 Buick Riviera, 1964 Chevy Impala, 1965 Chevy Malibu
      Muscle: 1970 Chevy Chevelle, 1966 Pontiac GTO
• 26 new races
• 12 new battle maps
• 10 new delivery missions
• 100+ new red light races
• New rims
• New body kits for each new car
• New vinyl
• Hydraulics/Airbags unlocked on all new cars
• New music

The paid DLC, or Premium Upgrade as it's known, will cost you $9.99 or 800 Microsoft Points, while you can still download the free version of the DLC which will extend the map, however won't give you any of the features listed above. Rockstar has stated that if you purchase the Free Upgrade, you will still be able to play against people with the Premium Upgrade.

Both the Premium and the Free versions of the Midnight Club: LA DLC will hit the PlayStation Store and Xbox LIVE on March 12th.

Update: Rockstar have now also posted news regarding the South Central upgrades, validating everything above mentioned in Trading Markets.

Source: Trading Markets