The paint isn't much in the scheme of things but painters cut corners since the job is labour intensive. Insist on only top quality paint and not the liquid chalk they like to use. I used to work for a paint manufacturer so I have knowledge of the trade. The answer is you must budget as much as you can afford to get the best return. To do a quality job requires one coat of primer/sealer and two topcoats and most everyone (including hired painters) will cut out one of the topcoats. The result is not pleasing. Get three quotes and pick the one that makes you feel the best about your choice which includes the painter. Ask for references.