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 General: Urgh, the ring I've been looking at is expensive, but sooner or later I'll have to pony up the dough.