Keep on exiting and entering the shop until you see the price of a particular fighter go down really low. Buy him/her then.

Max Payne

Hold L+ R then quickly press White, Black, Black, White, White, Black when at the main menu. You'll be playing the game with full health, unlimited painkillers, all weapons, and unlimited ammunition. The game's other cheats have to be earned by finishing the game.

When you're playing the game press start. Hold L and press Black(4), X(6), Y(3), Back. When at the main menu, go back and you'll hear a sound to confirm completion of a chapter.

When playing the game, press Start and enter White(2), Black, A, B, X, Y(3), R. You'll see +100 appear next to your health.