25 Nov 2011 at 04:12 - 5
1-handed double vamp weapons in the highest req, cruddiest skins, and non-max 14/-1 versions sell fast for at least 30-40k (might even be 50k or higher, I'm not sure.)
They're used as suicide weapons in some PvP formats and considered essential equipment there sometimes ... essential equipment which cannot be had from the PvP equipment panel!
The flashier skinned and req'd ones go for even more, but I'm not sure how much more. Given the recent bidding I've seen on Showtime's r9 Dual Gothic Axe, I'll guess your r10 Shadow Blade has at least 30e of potential to it.
Cheers & GL!