The PAX Promotion has now ended, but you can still buy access to the client missions of Season 1 at a reduced price of 15 USD, and later - when we know more about the exact date of release - you'll be able to buy Season 2 for 25 USD.
To all who bought the game for 35 USD - that is, before the 30th of September - don't worry; you will automatically get access to both Season 1 and 2!