I have seen a number of companies providing proxy clouds or IP clouds, whereby each of your web requests ultimately goes out through a random IP/proxy. You send your request to their IP and they forward it out through a random proxy, out of a pool of around 1000, for example, and return the response like a normal proxy.
They might also provide plain old private proxies, but it's the cloud (1000s of IPs) that I'm curious about. Some of these companies are very small, though. Several have cheap-looking websites and appear very amateur.
I'd like to get an idea of how these companies acquire such an amount of proxies and IPs. Assuming a company has a pool of 1000 thousand servers, each with one IP, OR maybe less servers but each having multiple IPs (extra network cards), it's still going to cost a lot of money to rent these, and take a huge amount of maintenance/management.
What is their trick? How do small companies like that obtain access to so many proxies/IPs?
I'm not curious about how they technically route requests, as it is a software problem.
EDIT: I am not talking about assigned blocks of IPs. These IPs appear completely unrelated to each other...