I searched online but AC adapters for the camera cost between $80 for a legit Canon one to $40 for a cheapie. I decided to build my own. More recent searches turned up even cheaper AC adapters (in the $10-$20 range) but quality is obviously dubious. If I am going to invest in some potential crap, it might as well be some crap I kludged together myself!
Note that while I performed this hack for a Canon 10D, this work can be easily adapted for just about any digital camera.
Step 1: Parts
Scrap battery of appropriate size for your camera
Wall Wart (AC/DC adapter) - 12V DC output
2.1 mm plug to mate with wall wart
LM317 - adjustable voltage regulator
240 Ohm resistor (I used a 220 ohm and it worked perfectly fine)
Small piece of perforated board - get one with rails!
Tools You Should Have:
Small-bladed hack saw
The tools listed above are just the ones I used. Feel free to substitute whatever you have that gets the job done. The work can be performed without a multimeter or bench supply but they are recommended.