I use Teresa Pritchard, who is based near you - she charges £40 - £45. As often as not that's for a quick check and some fine tuning, but she won't find lot's of mysterious ailments and spend an hour treating them.......
I pay £45 for an osteopath/physiotherapist (she is qualified as both). She is excellent and usually spends around an hour per horse. The cost is the same no matter how many horses she does.