The best way to get the best price is to set up a competitive bidding process from multiple dealers. Call multiple dealers tell them what you are looking for, tell them what you are doing is calling around to find out what each dealership wants as a mark up or mark down from invoice for a 2011 Mustang GT Coupe Premium (this is narrow enough that they can't say oh the price we gave you was only for this base Mustang but it will include any options you want). Tell them you would expect to be able to come on their lot and pick out any 2011 Mustang GT Premium coupe at the quoted mark up or mark down. Tell them you are only calling each dealership once, you will not disclose what the other dealers are offering (so they are all on a level playing field), and they must provide you with a quote in order to be in the running for your business. Doing this I got quotes ranging from sticker to $500 below invoice. There is a lot of great advice online for car buying tips. You won't know what a great deal is until you set up that competitive atmosphere. It is also best to call when you are almost ready, put the time crunch on them. Also deal with their fleet or internet manager. They are much more laid back than the floor sales guys and I think they are paid differently. Hope this helps. I don't know anything about the x-plan so I can't say anything there.