working on your assumption, why have a 6 point roll cage if you don't plan on rolling. the helmet i use in my car is the same i use on my bike. it is an arai and about £450 to buy on the bay. if only light use you can consider a cheaper option but less than £100 in my opinion and it is only an opinion gives you less protection, they are usually a lot heavier and are uncomfortable. what ever you decide ensure it is 'e' marked as some on the bay are not. these should not be used on a bike so the same should apply to a car.