I had requested the TrueCar price on some Durango’s in my area (DE, MD, PA) and for a 2018 SXT AWD with an MSRP of $35,130 the best I got is $30,666. That should give you a better of what to aim for.
I’m trying to figure out how you got to $259/mo–did they give you that number? I don’t know your specific taxes and fees, but with that sale price it looks like it would be closer to the mid $300’s.