Hi Josh,
Switching to 15" wheels will be easier.
There are loads of Focus's with ally wheels so you should be able to get a good set for sensible money. (see my note below about wheel nuts and centre caps.)
I would never use second hand tyres - there just too much of a risk so they represent no value but this can be a good bargaining point when buying especially as it'll cost you money to get them removed!
Rare or unusual/interesting wheels still fetch reasonable prices especially if they are in imaculate or refurbed condition and complete with centre caps and appropriate wheel nuts. Getting replacement centre caps and wheel nuts (especially the floating Ford type nuts or tube nuts) can cost as much as the wheels
Whereas wheels in abundance like those on the ford focus will never be more than scrap value as there are so many of them.
If your 14" wheels are rare and in good condition then you could get much of the cost of your replacement set back. - choose carefully where you sell them to maximise your return.
HTH BV
