So you want to create your own game games? This DIY Gamer Kit has you covered. It comes with an Arduino Uno, custom-designed PCB shield, and an LED matrix for 64 pixels of graphical feedback. It comes with pre-installed games, but you can change the code to create your own video games.
You are going to need a soldering iron to put this handheld game console together. Costs under $100 at this time.