Why the huge price differences in paints?

You can get some paints for as little as $5 a gallon and other paints are $40 or more a gallon. Here is a little known secret about paint...the cheaper the paint, the more clay that is mixed in as filler. Clay is extremely cheap. They mix it in to stretch out the quality ingredients, but what happens is that clay dries out, blows away and your paint just does not last. Spend the extra money and get that top of the line paint. Your paint will tend to last 5 to 10 times longer than the cheap paint, so unless you enjoy painting year after year - buy the good stuff.

Primer soaks into the material and seals it creating a better painting surface for the paint. Sheetrock, for instance, has paper on the outside of it, and it will absorb the paint and changing the sheen if it hasn't been sealed with primer first. Don't be fooled into buying a "primer-paint-in-one" thinking you get to skip a step. It will only work if the walls are already painted with a similar color and in good condition. If you are going from a dark to light color hit it with a primer first or you will be doing several coats with your expensive paint.