So when does the bidding end?

There would be no reason to ever stop bidding. To avoid losing your money, all you have to do is make another bid. Your opponent will probably realize that if he doesn't out bid you again, he's going to lose a lot of money. So he out bids you. Which really pisses you off, until you realize that you can avoid losing your money again if you just make another bid. The game goes back and forth until one of you dies of an overdose. Then the game ends by default, but the winner will have a tough time collecting his money from his dead opponent.