We know nothing about your Pathfinder other than the mileage, and your payments on it. So price the estimated Trade-in-value at Kelley Blue Book or a similar car appraisal site.
Then Go to this website:
Calculator to create realistic offers for a new car purchase (C) 2009 Ranchopedro
And punch in MSRP & Invoice (which can be found at Edmunds.com) from your customized Z.
Holdback for Nissan = 2%
Registration & Taxes = vary by state
You should get a rough estimate of where you should be...
Enjoy!