1) To pay up
2) To put money down
Originating from the latin word "Pone" (said like pony), which means money. The phrase Pony Up came from putting your money up on the table in a game of chance. Hence' Pone (Pony) up on the table.
In Poker: The ante's just been raise, so pony up boys,
In General: Urgh, the ring I've been looking at is expensive, but sooner or later I'll have to pony up the dough.