You are dealing with two challenges. The IP addresses and the software.
IP Addresses
The cheapest IP addresses I have found are at Co-Location providers. That means you own the server and you park it at their data center.
A /25 block of IP addresses, gives 125 usable IP's, cost $65 a month
Then you need a cheap server. Check EBay - HP ProLiant DL380e G8 SERVER LFF 2x XEON 8 CORE E5-2450L 1.8GHz 32GB RAM NO HDD $320 - 16 cores for $300. Add a 2-3 or 4TB Hitachi Ultrastar Enterprise grade hard drive for $120 or stick an SSD in it so that it flys.
Then CPanel and a Management Company to do everything to it (setup, security hardening, fix it, etc) $60 a month
Then you pay for the co-lo, anywhere from $35 month in Phoenix to $69 a month up north.
About $1.50 per IP and you own the hardware and you have enough power to hand as many domains on it as you want.
Software
You need a proxy server that cannot be seen.
It is called "High Anonymous Elite Proxy with Squid"
Here are two resources that explain it
https://www.metahackers.pro/setup-high-anonymous-elite-proxy/
http://www.dataparadis.net/osp/gnu-linux-server/proxy-server/high-anonymous-elite-proxy-with-squid/
If anyone does this, please write everything down, turn it into a journey and publish it.
I hope you enjoy this Mysterious Secret from The Eye™
Best regards,
The Eye