knox, alpinestar, technic, dianese are all good brands for back protectors.
i have no experience with icon and frankly don't plan on it after seeing some of their products quality, who knows maybe they have gotten their head screwed on straight and pumped out some good stuff.
there is also bohn which i dont like because they were known to copy knox's designs.
pricing: anywhere from 150 from your basic spine/tailbone protector to 250ish for the nice knox contour protector. regardless of what you get, you want to make sure that there are enough plates to cover your back, there are plenty of size charts that give you a range. also, if you get a spine protector, it'll take a few wears to break in just like anything else. so it may feel like your wearing a wooden board the first time, but after a while it'll feel like a part of your back.