Assuming you hold a BFTA card, it's £10 as stated above but if you don't I've just noticed this on the BFTA website under the GP rules:
"Anyone wishing to enter a Grand Prix Shoot who does not hold a BFTA card will pay an extra £2 and will be
entered as un-graded. The £2 will go to the BFTA".
AA Field Target Team 2007~2011
East Devon FTC - SWEFTA Club Champions 2006/2007/2008/2009/2010 & 2013/2014/2015