Snell Approved Racing Helmet

Go ahead and get a SA2015 car helmet, you can find them at a decent price at summitracing.com (Zapp helmets run $150). While some places allow motorcycle helmets, some tracks won't. Car helmets have fire retardant material while motorcycle helmets do not. Check if it needs to be full face or open face as well. While I swear by full face helmets for motorcycling, open face would probably be more enjoyable in a car (if you still have your airbags). I would imagine a fullface would get hot as balls in a car in no time, and you have to deal with visor fogging as well.

Get something cheap that meets the safety rating. The difference between a $150 and a $300 helmet is going to be negligible compared to what you get when you are spending Shoei and Arai money ($750+).

I've gotta pick up a car helmet as I want to do track days too...bummed I can't use my fancy ass bike helmet haha...Arai Corsair-V mmm

I would go ahead and get the 2015 personally. I don't know how often they phase out older Snell ratings, but I imagine the SA2020 isn't too far out. If it's a 10 yr kinda thing you know the SA2015 would be good till SA2025. I don't know for sure on that though.