In extremely expensive areas like the Bay Area, parking is usually either elevated or underground. Most of the buildings going up in Seattle spend 3-6 months excavating a parking garage.

If they aren't elevated or underground, the land itself is worth hundreds of dollars per square foot, so even if the actual construction is negligible the parking space is still worth $30,000+ that could be used for other things.

Even if a parking space is worth $30,000, amortized over 20 years that's only $.17/hour.

Well, anywhere that is popular enough to need parking (e.g. downtown commercial) is going to be more expensive than a standard house lot in SillyValley. A 5000sqft lot is easily $1M and probably more so you're going to need $200/sqft just for land. The minimum size for a compact parking space is 8x16 and area usage isn't better than 50% in a parking lot so you're at 256sqft before you start building anything... that's $5k.

(You missed a zero: 8×16×2×200 = $51k.)

I'm not familiar with the USA as much, but the number holds true for Australia.

A quick google found me this: http://www.vtpi.org/tca/tca0504.pdf

Table 5.4.3 - 4 Parking Structure Construction Costs might be what you're after.