Painters are in pretty high demand in greater Boston. Because they usually do all the prep at once, it ends up being disproportionately more expensive per sq ft for a single room than for a larger space.

For a single room, I'd try checking with a handyman too to see if they might do it cheaper, since they charge by hour of labor and the nature of their work means they may be able to squeeze in the waiting steps of painting.

DIY is also an option but when we did our place, with full time jobs and our (lack of) skill, it took weeks to do a few rooms. We hired a pro for stairs and for the rooms with vaulted ceilings and they finished in 2 days. So next time we are definitely just going to pay painters lol.