Will, the average price per square metre around here in Essex is £4, you could go with £3.
Before anyone states my last post was wrong with the figure it should of read £2,800 as I charge £4 per sqaure metre and not £3 lol
If you were to get it, get a high pressure high flow rate petrol washer and also get a turbo nozzle and wirl-a-way. the wirl-a-way stops all the splashing and doesnt leave any way near as much mess.
Matt