The Lush H'Suan Wen Hua hair mask is actually incredible...! It's £8.50 for 225g. I have longish hair (goes to my boobs) and it lasts 3 mask sessions. Just put it on dry hair, comb through, tie hair into a bun and put a shower cap on (warmth helps it). It says to do it for 20 mins, but I do it for 40 mins whilst doing my nails and stuff...

It's totally transformed my hair, don't get split ends anymore and have been able to grow it far longer than before.