First thing is to find an instructor around your area. a quick google search brings up a school in Glasgow (not sure if they are still active) or you could advertise for an individual a bit closer to home to train you (sure theres someone on here). training can be anywhere between £1000-£2000. its worth it and really is a must.
finding a pilot who would be happy to give you a tandem flight would be a bonus, its common for people to take their first flight and find its not for them.
once training is done its time to gear yourself up.
older gear your looking at- wing = £1000-£2000. motor = £1500-£3000
new gear, wing = £2500+. motor £4000+
after all that the sport becomes a lot cheaper, just fuel really.
happy hunting.