Get a custom. If you can find a decent shop they probably have "shop mixes" that are custom colors created in shop, and for more money they can/will do you up a custom color and then you'll be sure to have just what you want
Some cost more than others because of quality of the job, experience of the artist, and guarantee the shop offers. That's usually what it is based on. Don't skimp on a paintjob. If you can't afford a really good job, save up until you can or just do without. Unless your car is a rusted out shell, what you have now will probably look better than a horrible brand new job. Which is what you will get for "cheap".