The cheapest or should it be most thrifty person I ever knew, was when I was at university studying Optometry. The guy in question was a mature student, married with kids and had to work several jobs to pay for his tuition, family commitments and mortgage.
I never once saw him buy any food. He would collect everyones leftovers and eat those,even apple cores !!! He was a smoker and would collect all the cigarette ends, empty out the tobacco and then roll his own "new" cigarette.Tea was made with someones used tea bag.I could go on for some time but I think I have given an idea of what the guy was like.
He eventually graduated and even when he was earning a fortune, still carried on with many of his thrifty ways.