No wonder this country in its time has been dubbed "Rip Off Britain". Fair enough, vet's have a living to make, but that kind of price is disgraceful, especially for an OAP, lots of whom are on very limited budgets.
I'd get at least one other quote from another vet and would certainly be checking online, for example Petmed, there are quite a few reputable enough who could undoubtedly supply the requisite food a darned sight cheaper than above. It must be sprinkled with gold dust.