I got mine from amazon for about £15 but I've also seen them in john lewis for about £20
Sounds like a lot for a pillowcase but it's totally made a difference... I'd guess ebay might be cheaper? Good luck!
3b or c? Very fine hair but lots of it!
Newly CG (ish) and loving it so far, currently using Original Source to Co-wash, Australian Organics to condition, Trevor Sorbie curl cream and shockwaves gel. Weekly sulphate free shampoo.