You have it all wrong.
Say there is 2 players
Player A: Has 5m GP
Player B: Has 5m Junk and $2.50
Player B sends Player A $0.50 per mill of junk. Player A trades Player B and exchanges his GP for Player B's Junk.
In the end this is how it looks.
Player A: Has 5m Junk and $2.50
Player B: Has 5m gp