We get ours direct from Tassimo. If you like cappucino the cheapest way is to buy the 10 packs of Costa.
Once you sign up they frequently send codes. They average £4 to £5 for about 8 drink depending on what they are and there is a good choice. Atm we have Baileys Latte Macciato,Suchard chocolate. The Lor Kate macciato's are very nice.
I bought a Tassimo 6 weeks ago. I was researching models with the intention of buying one during Black Friday but Argos had one at £29.99 so I didn't wait. I bought a box of 40 Costa latte pods (plus the milk pods) from Amazon. Sainsbury's do 8 pods for £5 but seen on offer at £4. I'm only have the coffee at weekends and have a cupboard full of the pods so I won't go thirsty. I'm really pleased with it and it is so quick and easy to use.