Sit down and write a full business plan on how you get your business going and keep it going. And yes, even non-profits have businesses plans.
I want to build a site by developers for developers. I would make money by doing contracts myself, as would all developers who worked on the site.
We would all benefit by cutting out the middle man and offering a premium service where we can't compete today.
The overhead of a site like this is minimal and bandwidth costs would be paid on a volunteer basis (sponsored by developers/freelancers like me).
https://www.score.org/find-mentor
If you factor all that in you you have to charge 10%-20% to fund the base services?. If have an abusive client or contractor are you going let them go to harass? Yes, then you'll have low overhead but a bad reputations for not protecting your people. No, then you'll look restrictive and have a higher administrative cost.
Don;t forget admistrative costs. Your time costs money. It also keeps you away from working on contract.
Your point about 'designed to make the owner a bunch of money': you do realize that most of these site work on 1-10% profit margin with the owner putting in 60-100 hour a week for 5-10 years before they turn a profit if ever. Here's a good read on that:
https://quickbooks.intuit.com/r/financial-management/long-bu...
I really think you need to set done with a pen and paper with electronic devices turned off and write down a list of similar services. Write down what you like and dislike about them. Then write out what why they would do something you dislike.