Adding betting is a great twist on the Monty Hall idea that's makes it much more engaging. The presentation is also great. My one suggestion would be to add a way to enter bets more easily as going for any number that isn't close to 0 or the max is a bit annoying, either an onscreen keypad or a way to change the value of the increments (even just +/-10 in addition to +/-1) would go a long way.