A simple model? I don't know if it's simple.
But if you have a website you could be monetizing it in various ways. Google Adwords, selling ad banner space, selling pro memberships, etc. Then you can provide a reward system for participation. You might offer the ability to convert rewards into actual cash payouts. But you also create an internal store/system where people can spend their accumulated rewards internally, on ads, memberships, etc. This will be preferred because it helps you avoid writing checks, lol. The formula is you want more money coming in than you have going out. Some members will spend points internally. Others will let the accumulate and never cash in at all.
But if you have Google AdWords sending you checks each month for $300, and on average 10 people a month cash in their credits for $10 each, then you are profiting $200/mo. You just have to set a value to each post, reply, reactions, etc, so that you the payouts don't exceed your income.