Beacon climbing is cheaper.http://www.beaconclimbing.com/catalogue.php?cPath=5If you buy 100 individually on the website it will be £10. They mention bulk buying for lower prices as well but you can't do that on the website so you will have to ring them to order. The shipping will be cheaper if you ring them too.
I've always used IFS in Sheffield (can't find their website, 0114 273 7320).