Purchased my helmet at Parramatta. I was going to the big bike shop on the corner of GWH and Church St and turned into a kawasaki bike dealer near the corner of Parra Rd and Church St instead. Anyway, I picked up a cheap helmet for $130. I took everyones advise and tried a few on to get a good fit and size.
BTW, I did not want to spend over $200, as I would be using the helmet in a car for 20 min sessions and not on a bike. If I was on a bike, I'd have purchased a more expensive lightweight helmet, but I figured weight is not an issue when I'm strapped in and only doing about 5 hard laps at a time.
Murray - If your using the helmet on a bike and sunglasses are too uncomfortable under the helmet, you can buy a shaded visor for about $65 each to replace the clear visor.