https://www.theladders.com/job-listing/-72867907153225138/un...

This isn't exactly a direct source, but it's listing the hourly pay at 25.26$.

You wouldn't even need them to ride every single bus, just enough to deter weird behavior.

Even if hypothetically they cost as much as a real bus driver, this would be much safer. A bus driver doing overtime and possibly texting people isn't too hard to beat.