To clarify #2 in my other comment, I feel like they can be transferrable from account to account so streamers can give them away, but not be available on Tribaldex or the in-game market.

How about a 1-card pack for 800 DEC, also transferrable between accounts but not be available on Tribaldex or the in-game market. This still gives the chance for a GFL and should be pretty easy to implement. The more smaller price options the better.