I am not an expert painter, but my understanding is that paint brands like Benjamin Moore and Sherwin Williams provide better coverage and thus need fewer coats than some of the cheaper brands. You still need two coats, but with some colors in some cheaper brands you end up needing three to avoid streaks. But I'm hoping some professional painters weigh in here with a more technical explanation.

Sherwin Williams runs sales regularly where they do 20 or 30 percent off all their paint. SW and BM do cater to professional painters; they have a high quality product which allows professionals to get the job done faster with beautiful results. When you're paying for someone's labor, truly time is money and getting the job done in less time has a real monetary value. However, if you are doing it yourself and the time saved won't be directly translated into earning more money, covering the wall in one less coat might not be as important to you.

We use Pittsburg Paints for most of our work. They're significantly cheaper than SW or BM, but still provide the technical advice and customer service of a real paint store.

I would personally go for 30-35 dollars/gallon and spend the difference on high quality paint equipment. You will need a 2 1/2 or 3 inch angled sash brush (min $10), a good paint sleeve, roller cage and buy a paint pole, a 5 gallon bucket and a bucket screen if you're painting anything very large. It is much neater and easier to use than pouring the paint into an open pan. If you expect to be doing much painting, invest in an short extension pole because that makes the jobs soooo much easier!