Steve, who goes by USS Vision on the Star Trek Prop, Costume & Auction Forum, is selling off the Cardassian Rifle seen when Admiral Janeway is trying to secure technology from the Klingon, Korath, in Voyager's final episode "Endgame". The Rifle comes from the Christie's Auction, where it sold for $ 4,200, $ 5020 with the buyer's premium. Here is the Christie's Description:
CARDASSIAN RIFLE
A modified two-handed prop Cardassian rifle weapon made from solid cast resin with additional metal and resin parts -- 22in. long -- This Cardassian weapon was used in the Voyager series finale "Endgame, Part 1". It was the Cardassian rifle that Korath (Vaughn Armstrong) modifies to fire a Nadion pulse.
You can see the archived auction here. And read more on the Star Trek Prop, Costume & Auction Forum here. It is a beautiful piece, and I highly recommend it.
Alec