You can always expert invoice price (+/- $300) from any nissan dealer.
Altima is one of the best mid (full) size sedan, better than Camry (IMO).
If you want a Camry, you better get a V6. I rented a 4-Cylinder couple of years ago in Buffalo and almost killed me due to engineer/transmission hesitation problem. It was a pretty new car.
Good luck with your purchase!