Right now, ARIN IPv4 addresses are easier to get than ever before, as providers are handing out IPv4 addresses out like candy so that they have as much IPv4 space under their control as possible when ARIN runs out.

The next phase, as has already begun in the RIPE region, is where IPv4 addresses are bought and sold on the private market. Right now, they go for published rates of between $7-$15 per IP, depending on the size of the block they're sold as. This will probably go up dramatically once all the regional registries (and in particular ARIN) run out.

We'll probably then see the price of IPv4 addresses go up higher and higher, as utilization efficiency increases. It remains to be seen how high the costs will go, but it will probably get to a point where the costs of acquiring IPv4 will generally be higher than the costs of implementing IPv6. It will likely only be then that we see wholesale adoption of IPv6. Large portions of the Internet may begin using it before then, but the problem is that IPv4 will continue to be necessary until the whole of the Internet is on IPv6.

You do know IPv4 addresses are a mathematically limited set of numbers right? Once you're out of it, there's no "let's make up more numbers" or "Maybe we'll look in other dimensions" (funnily enough that's what NAT does). Not for oil, not for ipv4, and not for green parallel lines that form a red circle.