If existing old paint is not powdery and walls are not damp.. you can just paint yourself, ladder required of course. 18L paint only 65 bucks, other materials like paint roller etc also cheap. 2 18L tubs and roller, roller refills etc will not exceed 200.

As the labour price probably lumpsum basis coz small area also need time to wait for paint to dry. Labour exclude paint also will open price 1.2k to 1.5k thereabouts, hence more cost effective paint yourself.

4.5L covered two coats of a long living room 8m*3.3m in my experience. For colour paint.

Sealer recommended if walls are damp or existing paint is chalky.

18L cheap cheap only.. half the price is 7L if economy matex. Idk how the painter paint until super thin but the thing about economy paint it needs 0-1% dilution otherwise its runny and since its already pre-thinned to be cheap, the coverage sometimes need 2 coats if old paint is discoloured.