If the discount is from the manufacturer, like the $400, it usually is in addition to the usual margins. There is only so much wiggle room on the machines so the dealer pricing can only change based on volume discounts or other manufacturer price breaks. That said, the dealers have wider margins on implements and will often give you a super deal on whatever implement you need as part of that package. With interest rates low, if you can qualify, its a no-brainer to get as much as you'll need all at once.
Buddy of mine in Ohio caught the .5% rate in 2010 when he bought his L3800 and wrapped all his implements into the deal. The whole package is paid off now and he is so happy he got while the gettin' was good. Rates may not stay this low forever. But, qualification for financing is becoming tougher and tougher due to a looming credit crisis just around the corner.
Happy shopping!
Ray