How do I figure out how much to pay someone to paint a few rooms? Is there a formula for that? I will pay for all materials. All I need is labor. I live in New York city. Thanks

You don't have to figure it out. Call some painters, tell them what you want, they come look, you get 2 or 3 estimates and pick one.
Why can't you do it yourself and save the money ?

Painting a room, particularly with a roller, is very easy. Basic roller, frame and tray is $10. Trim out all the edges with a small brush. Google "painting with a roller" or You Tube the same topic. For average BR, DR and small LR walls, I typically get $150-200 +/- doing it as a handyman with furniture moved to the center of the room, light plates and outlet covers off, single coat, similar color, no patching. I never supply the paint but everything else. Are you considering ceilings too?