"...found stuff I forgot I had..." Have stuff that I don't know what it is or where I got it.
"...Ebay..." Evil, anti-firearm ownership, empire. Buying or selling there supports the people who want to take your firearms, of any kind, away from you.
A MK-6 Helmet runs 50 Pounds($80.63Cdn) in English surplus shops. They're not exactly common here. I'd guess(and a wild guess) $100 plus, here. You'd have to find somebody who wants it though.