I have both, basically the same pistol except the grip of the 6906 is .250" wider to handle the double stack 12 roung magazine. For a NIB, I don't see the $475 being out of line. Used ones on GB are listed for about the same. There is one listed now.
The only optional grips for the 6906, that I found, is the Hogue wrap around with finger grooves, which to me is too much bulk.