How about $4.50? That’s how much an hour at some meters in San Francisco will cost you. The price fluctuates, however, depending on how many near-by spaces are available, so the fewer the spaces, the higher the price. The meters use sensors implanted in the streets to figure out how congested the area is. The idea is to have at least one space available at all times.
The New York Times reports:

San Francisco’s parking experiment is the latest major attempt to improve the uneasy relationship between cities and the internal combustion engine — a century-long saga that has seen cities build highways and tear them down, widen streets and narrow them, and make more parking available at some times and discourage it at others, all to try to make their downtowns accessible but not too congested.

The city’s parking authority lets people check via computer, smartphone, and text on where and when parking spots are available, so theoretically, you won’t end up frustrated, circling the block and clogging traffic. As an ex-SF-er, who just got used to the idea that any parking within 10 blocks of my destination was considered good, I stamp this as “good news.”