I currently use Morrison's own brand inks for my printer because they're the cheapest I can find on the High Street (and they're also good quality). So it might be worth checking out Morrison's prices for the inks you require. (I find that most other supermarket's 'own brand' inks are far dearer than Morrison's)
However I used to use InkCycle and I've got nothing but praise for the quality of their products and their levels of service. (If you order right up to late afternoon, either online or by phone, your ink will arrive the following day - postal strikes permitting, of course!). Here are their price for the inks you require:
http://www.inkcycle.co.uk/inkjet_cartridges.php?cPath=140
/>
Chris