This post on the Battlefield Blog reveals the cost of the Onslaught mode (around $10/€9) but also mentions they’ll be selling BC2 kits.
Avoid the drudgery of unlocking weapons! Just give EA some of your (or your parent’s) hard earned cash!
Also this month, Battlefield: Bad Company 2 Kit Shortcuts will be available on Xbox 360 and PlayStation 3 for those players who don’t have time to spend levelling up to unlock all the kit specific items but still want to be competitive with those who have unlocked everything. The Kit Shortcuts will give you the unlocks available for kit each kit while still allowing you to progress through the ranking system as normal and will be available for 560 MS Points/$6.99 individually or if you want the whole bundle of kit shortcuts including the 7 available vehicle unlocks, 1600 MS Points on Xbox Live and $19.99/17.99€. The Kit Shortcuts will be available on Xbox Live Worldwide and European PlayStation Network from 16th June with the North American PlayStation Network having access to the shortcuts from 22nd June.
Next thing the Chinese gold farmers from WOW will descend on console games and do all the hard work of leveling up for us! more on reddit
Later! The Red Dragon has a good commentary on the new
map mode pack and shares a good idea about what to do with the extra revenue from those who buy the "shortcuts".