Depends on YOU as a negotiator, the MOTIVATION of the seller and many other factors, such as time of year, condition of the coach etc. etc. To try and use a mathematical formula is time consuming and foolish. You think mfg/dealers/sellers don't all these threads anyway. That's why these prices are out of whack. MFG/ well if they're gonna knock off 30% lets raise the MSRP by 35%..:S.
The MSRP on MY coach was $600,000. No way was that a realistic price. I.E. In Motion DSS system = $3400; Euro recliner = $1500; Power Cord Reel = $938; Sanicon system =$616...you get the idea. Inflate the price then negotiate it down and make the buyer feel like they're getting a good deal.
Out west we do the same with real estate. Dumb!..Funny how we don't consider MSRP when buying a gallon of milk or a good pot roast...:S....Dennis