If you have your receipts showing you regularly serviced the vehicle (oil changes), I would call Nissan direct to see if you can get any assistance. there are certain years of this engine that have issues with oil burning and leaking. If the oil level gets to low for prolong periods, such as extending the oil change interval, it can lead to damage of a key component holding the timing chain. If you do a search on the internet, you will see owners of Maxima, Xterra, Altimas, etc complaining about the timing chain issue.
Also the dealership is not the only place that can do this repair. I would check with an independent shop as well. If you live near a city, my guess is you can find a mechanic that specializes in Nissans. My guess is the repair will be cheaper than the dealership.