Welcome to NICO!
Since you didn't like the first reply you got when asking (and linking to) extended warranties, you're probably not going to be thrilled with this response. But here goes...
We have an incredible SEARCH
feature on this forum. NOTE: Info pertaining to first gen models often applies to second gen models as well.
--------> READ BEFORE CREATING NEW THREAD! <--------
I did the SEARCH
for you and found some useful information (links below). As for me personally, I wouldn't risk the chance that a spare fob off fleabay would work (there are fakes floating around on there), and I'd spend the money at the stealership to have it done right the first time. But you do you, as it's your vehicle (and money) it's ultimately your decision.
2015 Intelligent Key - One Car Only?
Key Fob Help
Nissan Keyless Remote Programming - Non-Intellikey
BTW, as you seem to know the previous owner, what was the excuse given for only handing over one fob? Have you tried going back to them to see if maybe they've managed to locate the second fob?