I just bought an X910BT on Amazon from Car Toys, $530. Since the purchase was from Car Toys (an authorized pioneer dealer), I'm hoping for the $100 rebate as well. I plan on calling them and asking for a receipt on Car Toys letterhead to send in with the rebate form.
$530 - $100 MIR = $430
EDIT: I just checked on Amazon, and CarToys has increased the price back up to $900, so this deal may not still be available.