As a DIY homeowner that paints maybe a room a year on average, my current favorite paint is HGTV Home Showcase by Sherwin Williams, available from Lowes for about $50 a tin. It has a red label. It's a small step up from the cheapest, but it's still far from the most expensive; but it seems to me that the gain in quality that you get from paying a bit more than the cheapest is much more than you would expect, so it's got a great quality-to-price ratio. With the cheapest paint, you have to work to get it on the walls smoothly, but this goes on nicely.