I just got back last week from touring Rome to Brindisi. Basically, I found everything Blackberry said to be true. The south has lots of cheap campgrounds along the coast. When I was in the interior, I usually just pitched my tent in a field (careful not to trample anybody's crops). If anyone was around I would ask permission, and the inevitable response was, "Sure, you can sleep wherever you want." In one small town they opened up the dorms in an abandoned school, turned on the hot water, and I spent two days partying with the locals.
The only problem you might have is finding a place to do laundry.
I lived in Italy for almost 4 years, and was a tour guide until 9/11. Email me if you have any questions.