It is currently on display in the Vienna Military Museum, along with the automobile the Archduke was riding in, and the uniform he was wearing. Here's the weapon in it's current display.
There are a lot of these pistols around, here's a fairly nice one with a buy it now price of $675.00.
The one Sherm wants is unique for the role it played in 20th Century history. I'm not sure how much the museum would want to part with it, but there is no way to price it and it's not currently for sale.