particular brush or foam roller to avoid brush marks.
Not a clue what a professional painter would charge for a job like this, as rates for painters vary by geographic region, years of experience, and complexity of a job (or lack thereof, as sometimes small jobs are less appealing)
Good luck to you!
here via brush using Defthane's interior polyurethane. Vacuum-assisted power sanding and tack clothing were utilized between coats to keep the air surrounding the project cleaner and mitigate surface sediment as the coating set up.