www.forddirect.com
Build your Stang, and take their invoice price * 0.996, then add $75 to the product. That is your X-Plan price.
Then you tack on Tax to that X-Plan Price, and finally take rebates off from that total.
Websites like Autos.msn.com and Edmunds do not take into account one of the advertising/commercial fees that is actually charged on all orders (something like $300-$400).
To sum it up, the Ford direct website's invoice price is by far the best value to use when calculating your X-Plan price. Do NOT go to MSN, Edmunds, or some site and argue with the Ford salesperson that XYZ website shows an invoice that is $300 less than what the dealership quoted you.