I have a tent in the backyard for only $599.99. No bathroom or kitchen privileges, no dogs. The bike is thrown in but it needs 2 new tires.
I'd guess your best bet would be to put an ad on Craigslist.org, since you wouldn't mind a non-traditional arrangement like a room rental. My guess is there are plenty of people who need a roommate right now with the economy the way it is.
You'll be wanting to look at the north end, the Morris Hill Bench area, the Boise Depot Bench area, and BSU area. I see there are a few ads in that area for well under $600. Good luck!