The bus driver is making what 60k maybe 90k a year? According to LA metro their new electric fleet is costing about $1.1m per bus. It would take over a decade for labor to exceed just the initial outlay. I'm not sure that busses are even used that long before replacement.

In terms of bathroom breaks, I've seen the driver pull over to use the mcdonalds or grocery store bathrooms so that is probably "free." There are only a few places in LA metro system where there is a purpose built layover facility where one might imagine there being a metro maintained bathroom facility. Most layover facilities are just dedicated street parking for busses to queue, such as the one at the end of Western blvd and franklin where I've seen the drivers utilize the Lazy Acres grocery store facilities.