Sometimes you're just paying for a slick roll mark... other times it's unique features, actual quality of materials, quality of machining, quality of finish or... all three. Discounting the cute roll marks, I can't think of any bare lower that's worth more than $250, and around $150 will get you all you'll need for a civilian AR.
You will get people telling you to get lower A or lower B or the lower with the groovy toxic avenger/skull and crossbones/other weird crap roll mark. Do your own research... then offer a list of specific lowers that you like to the forum. You'll get better and more objective comments.
Shoulder Drive Nicholson Club