Taking in to account whats been mentioned above. You need to look in to what racing you are doing. Because if you are still in a car with no cage, or harnesses, Im not sure what good a $1000 helmet is going to do you over a $200 one.
Anyway, I got mine from revoution racegear as above. Was $220 or so, unbranded and no fancy pants graphics. There is some rating that you need to look for, its basically the material the helmet is made out of, and how it absorbes an impact. As they deal with cars mostly, not motorbikes, prob best to go see them.
Also, you cant use an open faced at most gokarting places, so if you dable at that, keep that in mind.