I've still got a ways to go before I retire, but I'm privvy to a some of my grandmother's finances. I know she brings in less than $30K per year between her retirement and social security, but she's always got money left over so I guess that would put her in the $20-30K annual spending range.
Her house is paid for, so the biggest single expense she has is property taxes, which I think were around $2500. Then there's utilities...oil, electric, phone, water, cable tv. She also gives to the church, I think around $200 per month. No car, so that saves a lot. Then there's all those prescriptions and meds that seem to go hand in hand with old people.
Actually, the more I think about it, even $20-30K per year might be too high. She might actually be down in the high-end of that $15-20K bracket. She probably could be, except that my uncle lives with her, and she buys most of the food for both of them, and doesn't pay rent. He helps her keep the house up, though, and at her age (81) I don't know if I'd want her living alone, so it's a good thing he's there!