Economic travel

I am a student and I want to italy. To be honest I'm not planning to spend alot of money, Ive seen some cheap flight to pisa. My question is should I stay in pisa and go from there to rome and Venice because these ar my priority cities to visit. Or where should my accommodation should be ? Another question, I don't care about the accommodation as much as I care about the price, Im a student. So where can I find a cheap accommodations?