Per our logistics team, you get 5 gobbies (goblins stamps) per $1 you donate. You need 30 gobbies to buy back a logistics period (1 day of a game), so it breaks down to $6 per logistics period or monthly blanket. Each game has 2 logistics periods. In essence, $12 per game you want to buy back, but the Broken Shards campaign does has a level cap.
So to keep in line with the rest of the players you would only be allowed to buy 4 monthly blankets or 2 games (4 logistics periods) aka $24.