The rear brakes of a Ford Fusion generate about 30% of the braking
force, so they tend to last a lot longer than the front brake pads.
A set of new rear brake pads cost anywhere from about $25 to $50
depending on what you buy. I'd recommend ceramic pads since they
perform better, create less brake dust and tend to be quieter.
Here's the guide -
http://www.paulstravelpictures.com/Ford-Fusion-Rear-Brake-Pads-Replacement-Guide/index.html
I hope someone finds it to be useful.
Cheers,
Paul