Jap cruisers are awesome deals. Touring bikes that people took on one ride and never took it out of the garage again are usually nice expensive bikes that are great commuters.
80's superbikes like the GS1000 and cb900f's are less than a grand and usually just need tires and battery.
Streetlegal dirtbikes with street tires are cheap on gas and insurance and the most fun you can have with a helmet on.