Bike looks pretty good in the pictures - $3K seems very fair. I don't know of any W650-specific exhaust systems here in the US -- though there may be some of which I am not aware. There are several systems available in Japan and Europe. The best sounding one I have heard (on YouTube) is made by a Japanese company called Posh-Faith.
http://www.youtube.com/watch?v=K60L5zjw3xo