You can get a decent deal on trading and buying but usually it is much more difficult.
Many people have issues with looking at the total deal and doing the math to get to the point where it is a good deal for them.
Without knowing the new coach MSRP and what you're actually paying it is hard to say. However just realize something, you should be getting 25% off MSRP on the new purchase or more. End of story.
As for your trade, you figure the value, realize they are going to take some off because they need to make a profit and you're doing this for convenience or perhaps you need to roll a loan or whatever. Regardless, it will be less than if you sold it on your own.
You now have both ends of the deal figured out and the math either works or it doesn't.