There is no quick solution for you unless you go for that FM transmiter which will give you a very bad sound quality.
One solution is this OEM Car Radio for Ford 6000 CD MP3 which has mp3 capabilities and an USB connection on the backside
Secound solution is an original navigation for Ford Focus
Third solution is an adapter for the ford 6000 cd unit:
And of course there are a very large choice of aftermarket units that has all from navigation to bluetooth capabilities, touchscreen and more.
hope I could help