This is the cheapest i could find for a class 6 card.
Closest i could find is the play.com Class 4 card for 16.99.
I reckon the extra 3 quid is worth the performance boost. I'm due to receive one any day now. Will post test results.
(£19.20 with quidco 4%)
Tested transfer speeds and it is just over 8 Mb/s tested using an Integral USB SDHC reader.