I've got 2 month old MSI R9 280X that hash at 690kh easily - but I need $200 shipped.
I have 6 of them

Yeah I probably wouldn't be interested at that price. Going by the 3dmark scores of a 280x versus a 270x, I'd only be able to offer you about $140.
Due to being new/sealed, and "cream of the crop", I could bump up my offer to $125 (in btc, specific amount determined at the time of sending according to preev.com), but due to your lack of trust ratings, I would only be willing to pay after I've received it. I'll make good on my word. I've got years of positive reviews/trust, which you can look at in my sig below this post.
Keep the offers coming.
Please bear in mind, I have no plans to be mining the card. It'll be used strictly for gaming. If it's been mined on for months and you still want to sell it to me, make sure you run it through a vigorous testing of 3D, such as repeat loops of 3DMark, or Furmark, or OCCT GPU 3D with error checking enabled. I'll be doing the same thing when I get the card if its used, and if it fails in any way (artifacts, black screen, vibrating fans, etc), I'll be asking for a refund.