Just a little word of warning - I have no experience of using a cheaper one myself, but I've heard that they aren't really any good and tend to break easily, as the materials aren't of a very good quality. John Whitaker and Mark Todd do a slightly cheaper one though, and I think JHL do an even cheaper one that isn't too bad - check out Equestrian Clearance as they tend to have quite a good selection. The EquiAmi is also very good and is about £60 I think.