Think my vet charges approx £7 - £7.50, however if you are ordering more than one item Eg a pack of advocate and say a spray frontline my vet charges 2x prescriptions IYSWIM
And the other thing to watch is if you order 2 of one item they may well charge you 2 x presciptions
The last time I did a stock up got charged about 5 prescriptions from my vet
I was speaking to Hyperdrug (aka Canine chemists) about this and they said some vets do this and some will only charge one prescription for the whole lot
So I find the best thing is obviously only order the v.expensive things from online, its not worth upsetting your vet for saving a fiver
Its relatively easy to order via the presciption set up, you ring up with your order, then mail your prescriptions, they do not despatch until they have received them and checked them, I received goods in possibly 1-3 days after initial phone order, thats my experience with hyperdrug.