http://www.amazon.co.uk/Linksys-AE25...linksys+ae2500
£19.25 on Amazon with free delivery
Edit: here is an example of the type of cable you could go for
http://www.amazon.co.uk/Belkin-Cat5e...lkin+10m+cat5e
If you want a different length just search for "belkin 15m cat5e" as an example and you will get a list of results of varying coloured cable (which makes no difference) from various suppliers. There is normally at least one there with free delivery.