As low as $199 with a "qualifying plan" that starts at $40/month for 200 MB of data. Total base cost over the two years is $1159. Don't go too far over your plan though: It's $105 per gigabyte (of course, they market it as $0.0001/KB).
The $60 plan gives you 5GB data, and charges $503 per GB ($0.00048/KB) above that. Total base cost of ownership is $1639.
I'm not sure who goes for this. At the very least, AT&T should give away the netbooks.