Proxies can earn money on PPC, CPM and pop up/pop under ads.
Adsense for PPC
Adbrite for CPM
Adversal for pop unders.
I use Adsense and Adbrite for the homepage and use Adbrite for proxified pages. I also want to use Adversal for proxified pages.
Proxy hosts don't charge much.
Here are some examples
TMZHosting - Proxy Hosting Plans | cPanel, Fantastico, Fast Speeds!
Proxy Hosting | Proxy Host | PHP Proxy | Zelune Proxy | Glype Proxy | Proxie
https://cmodz-hosting.com/proxy.php