You can find the 13.4 in the USA from $265 ex tax, but you'll have to look for them. Shops are not allowed to advertise lower than the Minimum Advertisement Price set by DC which is around $290, but look for discounts or 'hot deals' on the websites. One of the cheapest shops I've been able to find around FL is
www.tropicaero.com, if you fill in an email adress they'll send you a message with the discount price of the article.
The best thing to do is to go to a shop with lots of headsets and try them on. Comfort is the first thing to look for. If you're willing to go for something else than David Clark, a suggestion from me is to have a look at the Softcomm C-90 (
www.softcommheadsets.com). It's a David Clark style headset, but it sells around $300 WITH active noise reduction (something you'll have to pay $600 for if you want a DC!).