I have the Tipperary Sportage that you posted, I got it from Legacytack.com for $50. Cheap yes, but I feel safe in it. I use it for jumping and trail riding, I personally wouldn't choose it for dressage, but at a local schooling show it wouldn't stick out like a sore thumb with a helmet cover. I don't know what kind of message BG is trying to convey by saying you need the most expensive gear to be safe? Just because a show helmet is expensive, probably due to the outside fabric/velvet covering and leather harness, it doesn't make it any more safe than a schooling helmet with coloured plastic outer and a nylon harness. If it is a ASTM/SEI (is that right for US) certified helmet then don't they meet the same standard?
I also use this site for tack reviews, maybe you can look up the good and bad reviews on the helmets in our price range to help make an informed choice? English Chaps/Boots/Helmets