PPL about £5k, ATPL exams £1950 at London Guildhall (23 weeks) or you can do a distance laerning over 46 weeks. IR costs about £10-12k depending on whether you have CPL or not.
Quite complex subject. Leeds flying school have a really good guide to becoming a commercial pilot with all the costs and requirements listed. Go to
www.leedsflyingschool.co.uk and click on the 'guide to becoming a commercial pilot' on the left hand side menu bar.
Email me if you have any questions!