I would pay attention to make in addition to maintainence. (Anyway, maintainence will be hard to know about unless they kept receipts for oil changes etc). Get ahold of the April issue of Consumer Reports, the annual car issue. They have lists of recommended used cars, cars to avoid, etc. These lists are based on the averages of comments from many of their readers on cars. I have found them to be a fairly reliable guide to the amount of maintainence problems I am likely to have.
My choice would be a low-mileage Honda or Toyota. You can get a better price on a Ford Crown Vic or Mercury Grand Marquis from the late 90’s, with decent reliability, but they are not easy on gas.