32 bit processors now cost $1. That means that you can build fairly competent video games for the price of a coffee. Check it out:

RBox: A diy 32 bit game console for the price of a latte – rossum’s posterous.

Addendum: The prototype is actually built on a small board that can be ordered from Digikey for about $30. The software is a teensy bit clever (maybe more than a teensy bit). It generates video entirely via interrupts, but the clever thing is that it uses the SPI interface on the chip in a way that allows you to generate the necessary chroma signals without overburdening the main cpu, which generates the luma part of the signal. Quite clever.