There seem to be different ways of obtaining a PTS card depending on which company is providing the training.
The PTS (Personal Track Safety) card is a requirement for anyone wishing to work on the railways.
PTS courses are classroom based generally and should be available nationwide.
It is possible to get a railways company that you would like to work for to sponsor you, I am assuming in that case that you would not have to pay for the course and would likely have a job with this company after gaining your card.
Courses start at around £175 and go up to around £450.
However, looking further into it I think the best way is to get a job/sponsorship first and the company will then provide the training. It seems that when you change to a different rail company you need a new card, so I would not advise paying for the course yourself before securing employment.