Prices don't really matter at this time.
The reason is, the exact price of ANY vehicle that Ford sells is not set until the vehicle is built and the dealer is invoiced. Ford can (and has) changed prices at any time.
If you are ordering a car now the best thing to do is to get an agreement with the dealer (in writing) for a specific price such as: $700 over invoice or $1,000 less than MSRP. That is the ONLY thing you can do a this point.
Take the closest 2004 Mustang configuration and add 5%. That will give you an approximate price for your 2005 Stang.