Italian Regions And Seasons
As with the other European destinations listed in this slideshow, prices will dip on rentals (and on airfares, too, for that matter) in the deep winter months, roughly late October through the end of March. July and August are peak season, so you'll need to book well ahead to snag a good rental then (be prepared to pay top dollar).
As for regions, in general, the further south you go, the less you'll pay. Head to Sicily, Apulia, Calabria, or Basilicata and you could wind up shelling out a good 40% less than you would renting a home near Lake Como or in Tuscany. Speaking of Tuscany, the neighboring province of Umbria has very much the same ambiance, wonderful art-and architecture-rich hill towns and cities to visit (Assisi, Todi, Spoleto, Orvieto, Perugia) but will come in a good 25% cheaper than its more popular neighbor, in terms of rental costs.