Most examiners charge around £100 - £200 for a renewal/revalidation fee. I dont think the average student really needs 10 hours(£100 sim/£300 aircraft) refresher training. Most people I know have all done it with 1 or 2 training trips. Also, most examiners tend to treat the revalidation with much more leniency and from what i've seen most seem turn the test itself into a 'training' flight.