Not sure how off KBB is in Alabama. (they do vary all over the country) Here in Illinois it's generally high. Generally about $2,000.
Dark 5.0....when the dealer thinks that you have a good understanding on how much your car is worth (retail) they will SHOW a higher trade in allowance to get you excited, so you will do business with them. There is quite enough mark up in the Cobra that they can show you a 2000 dollar over allowance and still show you a discount on the front end (the MSRP). Never the less you it still sounds you got a good deal.
People generally dont have an idea of what there car is worth unless you have the "black book" for that weeks issue. KBB gives a good information of what the cars is worth at publication, but the market changes on a daily basis and then at that point you really don't know what something is worth, and you get bit by the dealer. I recommend playing stupid and polite. And what ever they offer, play like you still can't offord it and don't be scared to walk away a couple of times.

But still get as much info as possiable and compare with other dealers.
