I have the Necksgen, it retails at only $599, adjustable,carbon fiber and made in the USA. No body straps, shoulder harness fits in slots and holds it in place nice simple design.
I use a collar designed for Kart racing made by Burris. Gives good support for your helmet while being relatively comfortable for about $35. Wont protect you in radical g-outs but takes a lot of stress off my neck with normal riding. Comet Kart Sales has a few different types of braces and collars.
+1 on the necksgen, I don't personally have one but I have spoken in depth with the owner on multiple occasions and he is a great guy with some great ideas and information.