I have heard good things about the Louise Galvin range, although I haven't tried it myself and don't know where you get it (possibly Waitrose although there's none near me). That was useful, wasn't it.
I use Liz Earle shampoo, it's £7.50 and I find it really good. You can get it online or in John Lewis. I sometimes use the Weleda Calendula body/hair wash and have always used it on the kids. I get that from a seller on ebay, zandk natural - they are excellent.
I think the Naked range mentioned above is the most budget friendly sls-free range available.