i bought Crysis 2 on steam when it was released. then Maximum Edition came out later, and it was a discounted upgrade for C2 owners. however this is no longer the case. im not playing ￡25 for the game again just to get the DLC, and im not sure how to buy the DLC on its own for the steam version. help appreciated

Sadly, the only way of getting hands on the DLC is by buying the Maximum Edition.

Just wait for the next Steam sale and you can upgrade to Max Edition for cheaper than what 1 DLC on it's own cost originally.