Cometh is a Free2Play game. In order to be able to play for free, you need a spaceship (MULE) and 40 cards. They are automatically provided once you register with your wallet to Cometh Battle. Every Crew Member has got the same base deck for the fairest experience.
Tips: It may be a smart move to keep interesting crafted cards you already have in your base deck as the 40 cards might rotate in the future.