Trading in a 2008 Altima Coupe for a Base Civic SI?

[mousebirdcow]

So I have my 2008 Altima Coupe that I got last August. This Altima Coupe is a Base 2.5S but has the extended warranty. The Coupe has roughly 7900 Miles on it. Now, I must say that I got ripped off back in August because I ended up paying 30k for the car after a 1k markup, financing, and of course the extended warranty. The car is in fairly good condition, some scratches here and there that make up a 1 year old car. I was thinking about Trading the car in for a New Civic SI Stock. The Civic Si Stock price they have is 21k. We probably owe 20k for the Altima by now. Its not really anything I have against my coupe, its just that I would like to drive a stick and I really like the SI's. Anyways, I was curious on roughly how hard I will be hit, and if I did end up doing this... what is the best way for me to do it.