Thanks for the input, guys. I ended up making one out of about $25 in parts. The extension cord was the most expensive part. I couldn't find much of a cheap one with three prongs. If I had gone two-prong, the whole thing would have come in under $10. With tax, I about broke even with the router speed controller from Harbor Freight. The Harbor Freight speed controller handles up to 1000 watts, while my dimmer only handles 600 watts. The speed controller also has an on/off switch as well as a dimmer. I figured that after shipping, I would still come out ahead, but it turns out there's a Harbor Freight in Knoxville, so I could have just picked one up. Either way, it's not too big a deal. I kind of like the "industrial" look of my home-made dimmer, compared to the professional look of the dimmer.
While I was building it, I tested out the wiring with a multimeter. The multimeter showed no continuity on the hot wire! I decided to just plug in a light bulb and see if it worked, and it didn't. So I pulled everything apart and started testing it all. Well, it turns out that AC light dimmers aren't simple rheostats. They have a diode in there that chops off the tops of the AC signal. So they don't show any continuity with a simple multimeter even when the switch is open. In other words, everything was wired up fine. So why didn't the light turn on when I plugged it in? Because the light bulb was burned out! Duh.
