Gear linkages don't usually work loose. They just wear out.
Open up the engine bay on your Focus, and have a look at the gear linkage. Grab the linkage rod and give it a tug. If the connected end moves around, then the linkage bush is worn out and needs replacing. Do not attempt to do this yourself unless you know what your doing.
When you try to put the car into gear, does it grind, or just not get into gear at all? If it grinds, then it will be either a synchro issue or a clutch issue. Replacing the synchros will require the box to come out. The parts will not be expensive, but the labour will be quite expensive.
It may be a clutch issue, with the clutch not having enough clearance. The Focus gearboxes (providing yours is an early "00" if i remember rightly?) are cable driven. If it IS cable driven, then the clutch clearance can be adjusted without the need for the box to come out.
From memory, i'm pretty sure it is NOT hydraulic driven, but if the clutch is hydraulic driven, then the lack of adjustment will mean that the clutch is worn. This will require the clutch to be changed, which will mean the box will have to come out. The clutch won't be too much (Should be no more than £100 for the part) but as above, the labour will be quite steep.