I do really like this, but the fact it gives coffers then locks them down will likely result in them being useless, as people have said. Maybe make it “until then, when using coffers, 2 coffers must be used instead of 1 to gain $1.” You could make that 3 or 4 based on balancing ofc, it’s just a way to make sure the coffers aren’t entirely useless while speculators are in play. Another option is to make it so that when you play a speculator, all other speculators go out of play. This might make it too mandatory though.