David Strom:

For the past 27 years, I have owned a class C block of IPv4 addresses. I don’t recall what prompted me back then to apply to Jon Postel for my block: I didn’t really have any way to run a network online, and back then the Internet was just catching on.

Apparently, there’s a mature market for buying and selling IP addresses and even a rental market. Read the post for specifics on the marketplace and on price.