MSE charge £40 per box for site paint, with no entry fee. Or you can pay £15 entry and you can bring your own paint. Site pyro only. Site paint varies but sometimes can be fairly low quality, lately they have used GI 1* more often than not, which is good enough, but don't be surprised to see Polar Ice (a winter paint) in the summer!
Mayhem Essex charge £55 for entry (£50 in advance), which includes a box of paint. Additional paint is cheaper, something like £25-£30 per box. Site pyro only. I believe they use Sterling Shield paint, which tends to perform fairly well in the woods, but my last visit was a while ago.