Toddle on over to Freedom Ford on Military Highway and talk to Mark Vasiloff. You aren't going to get one at Invoice anywhere, but Mark will order ya up one at MSRP which is the best deal your going to get for quite a while. There is only a $2300 dollar difference between invoice and MSRP on the 2006 Ford Mustang 2dr Convertible GT Premium anyhow.
Now if you want a helluva a deal on an F-150 Mark is definitely the man as he put together the deal on my 05 F-150 STX last February for about 8k off invoice.
You can also e-mail him at snipped-for-privacy@freedomauto.dealerspace.com