Hi. I would recomend Ebay for some 13.4, but ask about your flying club, lots of people have 13.4's and when they come to upgrade, they arent needed anymore, so some cheap potentials there.
Also to just go a bit mad, have a look at nanocomm GA, by puretone. They are a new kind of custom made in ear system. where you have custom ear cast's taken and have a bespoke headset in the end. It's very light, cancels more noise than you DC's and cost roughly the same. I am considering getting some myself.
All the best
jon