It also confirms the HP307 on eBay for 3400 incl shipping is overpriced (but is selling... They have 1 left. Glad I found you).
Mac's suggested discount is arbitrary and probably reflects his experience. It's not truly tied to any cost/profit/discount formula that is standard or necessarily common.
Since shipping charges for a large console DP can vary significantly even within the US (I shipped a similar-sized console from Atlanta to Montana and the shipping & insurance charge was $419, UPS & FedEx were over $550), the ebay price (including ebay fees) is MAP + a fee to subsidize the shipping. Items like that are often classified as LTL Freight, sent by the big trucks, i.e. expensive. After credit card fees, my profit on that particular deal was seriously like $40.
My example definitely reflects the higher end of shipping as others will be less that $200, but the ebay seller is taking a gamble that it isn't going somewhere too remote.