About $10k/mo gross revenue and takes a few hours of work a week (unless there’s a downtime event that needs fixing). A lot of upfront work to build some of these systems though.
Got to $2k/mo in the first month of doing this. I don’t recommend working (as a solo operator) with clients who have budgets less than $5-10k/mo. Too much overhead for too little return in that case.
In what little spare time I have left after my day job and looking after two small kids, I put more automation in place to improve reliability for my clients and reduce my own ops time requirement.
I get leads for this by referral from people I’ve done good work for in the past. But it’s the kind of thing you could bootstrap by direct outbound sales, publishing authority-building content to the right business audience, going to conferences/trade shows, or building a referral network from other service provides.