The problem you will find is that not many are available in the second hand market, and the ones that are will be industrial and still silly money.
I have hired a duplex to degrease a couple of pub kitchens and to be honest I was not happy with it. The steam misted up the job and you could not see what you were doing half the time.
We ended up doing the job by good old fashioned elbow grease in the end, with much better results. You have to remember that the guys flogging these machines use very clever marketing strategies, and make them out to be something they are not most of the time.