Yes you can sign up that day but it's $10 cheaper if you pre-register. Link to pre-reg page is in the first post. If you want to run for points you will need to be a NASA member, which also makes each event another $10 cheaper. Nonmembers appear on the results but not in the championship standings.

You can get the membership when you pre-reg. Sign up for the member price and the system will automatically add a membership to your cart.