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As long as you can deal with good public transit instead of great public transit, I can think of a few places. By good, I mean buses that run well into the evening hours and on weekends. They may only run every 30-60 minutes during non-peak times, but you can still get where you want to go with smart planning and patience.
One plane that comes to mind is Reno, Nevada. I lived there for a while. Some routes run 24 hours a day, while others run pretty late. Popular routes can be found every 15-30 minutes. I lived there on less than 25k, and so I know it can be done.
Like others have said, Spokane has a decent system for a city its size. It runs until about 10 or 11pm. Colorado Springs and Tucson also run until about that time, and will be more affordable than the West Coast cities.
If you live/work in the right parts of the city, Albuquerque could qualify.
Public transport is improving (and already adequate, if not yet exceptional, within a certain range) and great strides are being made to make it cyclable with networks of bike paths, bike routes, and bike boulevards. The walkable areas are also those that are adequately served by public transport. There are however vast areas of the city that are under-served by public transport, but a lot of the affordable and fun residential areas and commercial areas (jobs) are.
Salaries are relatively low but so is the cost of living. We have not been as hard hit in the recession, especially in terms of unemployment rates.
Nota Bene: I wouldn't move to any city based simply on its reputation as being conducive to a car-free lifestyle, though. Check your potential destinations in person if at all possible and do your research.