Most tracks just require an M95 rated which you can get from 79 to 150+
If you plan to road race go for an SA 00 which can be had for $130 to $700
You need to decide if you want full face or open face (like Big Dale wore most of the time). You might feel more comfortable in open face but if you are going to hit a road course I'd suggest full face.
http://www.jegs.com http://www.summitracing.com http://www.helmetcity.com http://www.racerwholesale.com http://www.simpsonraceproducts.com
or your local speed shop.
I have a simpson open face I bought and used one season that I do not use any more as I switched to closed face. If you fit an XL helmet I will sell it to you at a fair price and can even bring it to you as I am in Covington and Newport Mon - Thur weekly.
[Modified by REDGAR, 8:23 PM 11/3/2002]