The technically easy way is to become a proxy-reseller.
There's quite a lot to hosting the proxies yourself, but a subset of what's involved:
1) identify and buy the proper hardware
2) Buy the requisite IP space/data plans
3) write/configure the software
- auth, http(s) + socks5 support, and ip-rotation features at a minimum
- security, performance, and scalability can't be skimped on, especially security
4) Set up the systems
- 1gb internet at the very least
- Once it's up and running, you'd really rather not have to take it down, so make sure your setup can run indefinitely.
- Watch out for fires if you're setting up phone farms (or really any self-hosted cluster that runs 24/7)
5) set up an eCommerce site
- Need some kind of dashboard for users to keep track of and administer their proxies
- Must have some kind of trial code support
and then marketing. Just fyi, if you are unable to use proxies to make money yourself, it's doubtful you have enough understanding to meet your customer's needs. So step 1: learn how to use proxies to make money, meanwhile, you can get up to speed on the network engineering, security, and webdev skills needed to set up the business. My guess is at that point you'd probably rather just use them yourself, which is why I wonder if it makes financial sense to try and become a proxy seller unless you already have the required technical skillset. Like, if proxies are useful enough to be worth selling, and you don't already have the complex skillset to do so, it seems like you're better off just using them to make money, but go for it if you find it interesting! Obvi this is all without knowing what your competencies are, so go with your gut.