Well, from my vet, they're around £3.50 a sachet inc VAT but it depends on how many a day you are giving. A 10-day course of two sachets per day cost me almost £70 a few weeks ago.
I paid £33 for a 5 day course of Norodine granules. Thats a box of 10 sachets given twice daily.
Incidently farmer friend let me borrow a box when I ran out over a weekend. He'd got his for less than half that price.