After watching Bobby_M's youtube video, I decided to build my own immersion chiller. I ordered 50' of 1/2" tubing from coppertubingsales.com. $43 shipped, which is a lot cheaper than the big box stores.
I had some 1/2" straight copper pipe left over from finishing my basement, so I picked up some 1/2" to 3/8" reducers to attach to the refrigeration tubing (thanks Bobby_M for the heads-up that refrigeration tubing is measured by O.D., while straight tubing is measured by I.D.).
The only part I had trouble with was trying to solder 5/8" barbed garden hose adapters. I drilled them out to 1/2", but could not get a leak-free connection. After trying to re-solder several times, I gave up on that. Instead, I had some 1/2" threaded adapters that I soldered onto the ends of the tubes and picked up garden hose adapters that fit onto the threaded adapters. These were Watts A-660 (female swivel hose adapter) and A-668 (male hose adapter).
It passed the leak test tonight. I washed it in soap and water and will boil it in a water/vinegar mix tomorrow morning and let it sit for a couple hours. Then, it will be ready for it's first run tomorrow night. Can't wait!