FYI: Just called my local costco, the person I spoke with said it's a warehouse sale only (so online only), they didn't even have any in stock. He did confirm the price though. He also confirmed it comes with the rolling cart ($50 value), an extra 50 feet of hose, and 2 replacement cartridges. This sells for $449 for the unit alone, then $90 for the replacement resin and $25 for the hose... almost $600 retail.
Seems too good to be true, so I am wary that this may be a mistake on Costco's part and they might pull the deal and cancel orders.