There are several factors that determine the cost of paints. While quality can play a part, there are other factors that make a difference too. Kathaleen explains~
Paints with colors (pigments) that are readily available and more abundant are the cheapest, like earthy colors that come from clays or dirt i.e. raw umber comes from Umbria, Italy and burnt sienna comes from Sienna, Italy. Paints whose color comes from rarer earth elements are more expensive like the pure reds. (there is not much in nature that is bright red except for the cardinal) Also, paints with pure pigments (no mixing with any other color or medium) are usually more expensive. Thus Color (pure) cost twice as much as Color (Hue). To the naked eye the color from each tube can look identical – the BIG difference is when you mix this paint with another color. Think of a thin sheet of colored glass laid over another color with the end result being a vibrant, clean new color. But if you use a hued color, the end result will be grayer and more opaque (can’t see through it) color. In other words, pure pigments are transparent and used for mixing, while hues are for using as is. Better made paints are given a SERIES number, usually 1-4.