I'm pretty sure, that color is also known as "plum"?
If so, Asda sell it for £6.00
Or... check Ebay. I did a quick search and, although the listings have no ended, a couple went for no more than £3 with free delivery!
There are quite a few shops on there that have the full range for sale. You'll have to look through them all though, and find the ones who stock that particular color.