By APC I guess you're meaning an Assessment of Previous Competency course. You only need to do this if it has been greater than 6months since you either obtained your aerodrome rating and you have done no training since then, or longer than 6 months since you trained in a tower. There are 2 courses I know of. Both of them 3 days. NATS one will cost you in the region of £5k for the course, college at Rudloe in Wiltshire just under £1k. You come out of both courses with the same qualification, depends how flush you're feeling I guess.