Walmart has a good selection of paint for $12 - $14 per gallon, and rumor says that it is actually sherwin williams that has been re-labeled. If that is still too expensive, you can visit paint stores and get miss-tints for about $2 per gallon. Because they are all different colors, one thing you can do for a large quantity of the same color paint is to mix it all up in a 5 gallon bucket. Very easy to create various shades of battleship gray, and then you will have a large enough supply to complete your project and do touch ups. Another thing to do is put down 1 coat of the cheap miss-tint, then coat on top of that with a color you purchased.