Starting April 2nd, Perpetuum will be dropping its subscription payment model to move forward with a single-purchase buy-to-play model priced at 28.99 USD/EUR. There will also be in-game item purchases that will include "previously unavailable services and cosmetic upgrades."
As a special bonus for anyone who has ever paid for at least three months of the game's subscription, the game will be completely free. Be sure to check out the most recent blog post for more details on this new payment model and changes coming to the game with this Steam launch on April 2nd.
[Thanks to Fredrik and Zoltan for the tips!]