Painting one room will always be unreasonably expensive because you’re paying for a 1-2 man painting crew’s entire day.

It’s not like they punch out and you don’t pay them while they wait for the primer or first coat to dry a bit, and they can’t just move on to another room.

It’s also rare to have such a small sized job so they can’t just jump to another small job and come back (you wouldn’t want them to anyway).

What you’re paying for if they’re pretty decent painters but on the low end is is probably $35/hr. is 2x 8hrs x $35 = $560 for a crew of two for the day.

Paint has gotten absurdly expensive too.

So based on your dimensions and assuming 8’-0” walls, one door and two windows and trim at the base and frames - about 3 gallons of primer and depending on your trim color, 3-4 gallons of paint.

Call it $50 for Primer and $200 for Paint.

Add 20% markup for them having to get the paint, and another $100 in overhead charges to cover their supplies, etc, and you’re at $560+$300+$100

So that seems fair.

My advice is (if you can afford it, I know you’re expecting) think about having another room painted, you’d probably just be paying another $250-300 in materials.