Totally agree with Pearl. Blizzaks. All four wheels. Go to Tire Rack and read up on why you want all four corners the same.
There actually is another reason for all four - speed sensors with the brakes. You will drive the car crazy trying to stop. The winters will be a larger diameter than the other tires. It will drive the ABS crazy, and you'll have super strange nasty braking (as in really harsh). I ran into that problem with our most recent FFE. Somebody put a brand new junk tire on to fix a flat before they turned the car in from their lease. The new tire was just enough different from the other three that the car acted crazy while braking. It felt like the brakes wanted to grab all the time. Couldn't ever stop smoothly. All new tires, the problem went away.
And I wouldn't even bother trying to find a better price, just do the full set from Tire Rack. They ship quickly to your house, completely mounted and balanced, ready to put on the car.
Not sure why you want winter tires, but that's OK, your choice. I personally hate the whole nonsense with storing four tires and changing them twice a year. It is irritation for not a lot of better handling in the snow anyway.
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