Angry Birds

I know it's unoriginal, but hear me out. The Angry Birds cost $100. For one game, it will produce one of a certain tower every 10 rounds (or minutes, whichever comes first). This includes all birds from the versions of the game.

Birds
Red Bird: Creates a Ninja.

Blue Bird: Creates 3 dart monkeys.

Yellow Bird: Creates a Sniper.

Black Bird: Creates a Bomb Tower.

White Bird: Creates a Mortar.

Boomerang Bird: Creates a Boomerang Monkey.

Big Brother Bird: Creates a Spike-O-Pult.

Orange Bird: Creates a random tower costing less than $800.

Pink Bird: Creates a Monkey Apprentice.

Ice Bird: Creates an Ice Monkey.

Pro
After 45 buys, you gain the Mighty Eagle. This gives the ability to deal 10000 damage to all bloons on screen. This takes 5 minutes to recharge.

Very rarely, you won't get the ability, but you will gain the permanant Mighty Eagle. Every 20 rounds (or 15 minutes), a Supermonkey is born!