I second this idea. I always get mine done in Lao Jie, two stops up the Metro in Shenzhen. 35 RMB for a wash, head massage and cut. Then, of course, you should make a day of it - eat 'till you burst for 20 - 30 RMB; load up on Sichuan spices and impossible-to-find-in-Hong Kong ingredients for under 20RMB; pick up some core supplies from the 2-yuan shop; treat yourself to a 35 RMB foot massage - and the whole day out should set you back only a hundred or so RMB (plus train fare).