DISCLAIMER: This is a lo-fi wireless audio system. In my mind, the sound quality and the freedom of motion is worth way more than what could be expected from about $5 and ten minutes of work, but these things tend to be subjective. If you want pure clean sound, you discriminating virtuoso you, save your pennies and spring for the $450+ professional version.
DISCLAIMER. Part II: Yes, I did actually make it, and it works. Sheesh...
Step 1: Get your materials
1. A set of walkie-talkies. Just about any variety in good working order will do. I found my "kiddie" style National Geographic walkie-talkies, batteries included, at the swap meet for a paltry $5. I'm sure I could have gotten a cheaper pair if I had been more patient, but I was rearing to try my idea out, and $5 seemed reasonable.
2. Two 1/4" audio plugs, male or female, depending on your preference. I actually just cut a guitar cable in half, and that worked out pretty clean. Doesn't really matter, basically you just want to run the signal from the guitar to the "transmitter" unit and from the "receiver" unit to the amp.
3. Solder, flux, soldering iron, maybe some hot glue. You know, the usual junk.
4. Might be good to have a Churro around, just to nibble on something between steps.