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I've got a Karcher K2 which is the cheapest model and ~ £60 I think. Plenty powerful enough to get rid of most muck and also risk washing out the grout.
I did end up buying a few extras (the patio attachment and variable wand) to make it more usable so you may be better getting a set with those in, although I generally got them by setting up price alerts and getting them when they were cheap.
pressure washers - talk to me. are the £60 bosch/karcher ones crap or do i need to be spending >£100. occasional use only for cleaning patio etc.