Also, don't be afraid to 'fudge' the numbers a bit before shopping around. As in...make a number that you find reasonable (or any of the ones you find on the forums for reference) and go shopping with it. Make them work and sweat to make that deal.
Case in point, I F/O a 2013 just a few weeks ago.
MSRP - $46,639
Minus Discount(s), etc - $38,750 + GST/PST
This is in Canadian funds, but it can compare closely.
2013 Mustang GT - 402A GT/CS - 6R80 - Glass Roof - Engine Block Heater - SGM Exterior - CB/Miko Interior
Steeda Adjustable PHB (Street) and Steeda PH Brace, Stainless Works Retro Catback Exhaust...