Regularly on offer at Amazon. Probably best to set up a camelcamelcamel price alert like I do. Also a great add-on purchase to push you over the £20 mark to enable free delivery.
I've been using this for my Delonghi coffee machine for a number of years - 100+ great reviews from other users.
I hope this helps someone.
Removes coffee residue and limescale
Suitable for all machine types
Effective non toxic formula
Improves machine performance saving money
Currently £3.79 at Homebase