Another NASA sponsor to consider is Apex Performance. They offer a 10% discount to all NASA racers, which would be at least $70 off of a HANS, depending on what model you get.
Also, +1 to what Chuck said about the sliding tethers. Not only do they work extremely well, but they're much cheaper to buy with the device ($15) than to buy them later and add-on ($75).
CJ - the 20 degree model is the one to get. I would think that the 10 would be way too upright in any kind of sportscar.
