Cashies generally don't know what metal CDs are worth. I picked up a whole heap of Enslanved and Darkthrone for $4 each. Granted they're a little beat up, but at $4 that's what you'd expect.
I got a mint copy of Metallica's Jump In The Fire/Creeping Death EP on CD for $5. Shoulda seen the guys face when I told him what it was worth as I was walking out of the shop.
no way i got the exact same cd from cashies about 8 years ago, only payed $3 for mine though
, also have an original binge n purge box set, still in its plastic wrap n everything, that came from a second hand place somewhere in mandurah (relative spoted it for me) that i got for $50 about 3 years ago.