I just did this over the last few weeks...just some tidying up left to do.
I bought a "Fuzeblock FZ-1" which gets wired directly to the +/- of the battery and used a piggyback fuse on the horn fuse to connect a wire for the switched power relay. The FZ-1 is installed in the empty ABS space. The autocom gets wired to the FZ-1 so that it only comes on when the ignition is switched on. I've also wired the GPS (2820) power and heated gear plug into the FZ-1 as well.
The Autocom is installed aft of the bike's fuse box (tool pouch had to be removed) for easy access to adjust volume and VOX. My MP3 player and BT dongle is there as well.
Works pretty good even with earplugs in, and yes, you will spend a lot more on the leads depending on what you be connecting to the Autocom.