With 9 to worm I buy them in bulk & I've just been doing some research this morning as need to do mine again. I am yet to find anywhere cheaper than Hey Farm Saddlery as they offer free P&P combined with a good price - some of the other bulk sellers charge a lot for their P&P when you start to look in to it.
I get mine from the Vet. It's the only place they are available I have found, as over here there is quite strict control of drugs. Supermarkets don't even sell ibuprofen. Have two to do, buy one tube as they are both lovely horsies and their weights fit perfectly with the amount
Only available from vets here. My vet's wife is terrific. I just turn up at the house, ask for a wormer and she gives me the appropriate one for the time of year, bearing in mind which wormers have been used previously. Great service.
Buy in bulk from Mile End (advertised weekly in H&H). Usually ring up a few more at the same time but Mile End will always meet the cheapest price you've found.