From the Order & Chaos Online FAQ:
The initial purchase includes three months of play time; after that, additional months cost $0.99, 3 months for $1.99, or 6 months for $2.99.

Alternately, could you do a $1.99 PIA that gets you access to a majority of the game's ships for the course of 1 month?

I'll add that this is the first/only iOS app that I've really been looking forward to playing.