I know I've seen those kits on eBay, and reasonably priced, if I remember right.

Avoid cutting off the factory radio connectors if you can. I wish I had. I was young and impatient, and had to have the radio hooked up right then! What a dumbass. It's much easier to wire up a new head unit to an adapter and then just plug it into the factory harnesses, than it is to have your hands shoved inside the dash, trying to connect wires.