£5 for the outside £8 with the insides. But I am in 'Sarf' London and you can get more there. If you were in Blackpool then £3 would be tops. If you were in Richmond on Thames or Guildford then £7 easily achieivable.
Each area has its own affluence limits and you cannot give a national price. We are not Teachers or Police officers (although I would love their pensions!)
The frosted every now and again when needed is a great clincher and not too onerous as I would expect this to be done 3 monthly most......