Funny you should ask, I just went through this.
Don't just buy one new tire. The used FFE we bought had a brand new super cheap tire on it (the person that turned the car in for lease end probably had a flat and didn't want to spend money on all four tires, so they bought a super awful super cheap single tire), and paired that with the three tires from the factory with 35,000 miles on them. Guess what, the car acted terrible with that mismatch - grabby brakes, some pulling, and lots of tire noise.
I just had Costco do a set of 4 same as from the factory Michelins. They were doing a $70 off a set of 4 and $0.01 per tire installation. That worked out to around $740 for the four tires, installed with tax and disposal fees.
Frankly, we've had three FFE's, all had the same Michelin tires, they all drive perfectly well, get good range, are quiet, and wear well. I wouldn't change a thing.
2014 Platinum White FFE (Turning in mid Dec. 2016 25,000 miles)
2013 Ingot Silver FFE
2012 Titanium ICE Focus
2014 Tesla Model S 85