Be careful of who you get to do this work. I bought one and contacted an electrician. He said he could not install it as the house needed to be re-wired first. I got a second opinion and it was much the same as the first. �3,000 later and the house is rewired and we have an electric shower.
My friend had one installed just the other week, to have the plumbing part done it was �120 and the elcrtics was fairly simple only �30 but again it depends on your electrics and plumbing etc. It's different for everyone.