One gallon is more than enough
One gallon of the West Marine ablative paint put one coat on my Oday 23, with enough left over to paint the bottom of my father's 14' Boston Whaler. After two years, in LI Sound, I only needed one coat! I love the ablative paint; all that needed to be done was to rough up the existing paint with sandpaper, tape off the waterline and roll on the paint. The whole job took about two hours. I recommend painting a little extra on the leading edge of the bow, rudder and centerboard. When they block your boat, have them set it high enough so that you can drop the centerboard as far as possible to make the painting easier. Sometimes they don't like doing this because they can't have the boat rest on its stub keel (the most stable resting position). However, if the boat is only out for painting, it shouldn't make a difference. Get a couple of those small foam disposable brushes and paint as far up into the trunk as you can. You may have to file off some barnicles first, but this little extra is worth it. Also, for painting in the trunk, DO NOT USE ABLATIVE PAINT. Use hard-shell paint as the ablative paint needs to wear off to be effective. BTW, the prices quoted sound pretty high. If your yard allows you or other contractors to work on your own boat, I would check for independents. Ask other owners for recommendations; I know a guy who advertises as a car detailer, but also waxes boats. He does a great job for about half of what a yard charges. Yacht clubs that don't have a full-service yard of their own are great places to find independent contractors. The clubs in my area allow these guys to work on members' boats, waxing, painting, engine work, etc. Just check the club's bulletin board for their cards, or ask any memeber. Good luck.