I have added after market cams to both Dodges and Fords.
Coastale Tek makes a good camera with plenty of cable. I am sure there are other brands/companies out there. Find the AV hook ups, mount the camera and be sure to route your wire securely. Less the 100 bucks.
2012 Focus Titanium HB, Sterling Grey with 401A PKG, Titanium Handling PKG, Moon Roof, Winter Kit & MFT w/NAV.