It costs about £40-50 to detail and correct a car in materials alone, not including the cost of the machine, premises, water, public liability insurance and what not.
I absolutely guarantee it will be terrible afterwards.
The amount of cars we see which have been "machine polished" by Dealers/Cowboys/Valeters who operate at the local garden center is beyond a joke.
Before I stopped doing private work I would charge around £120 for a decent correction, but that was mates rates and more because of how much I love detailing, it'd also be over a couple of days in most cases
These days it's not worth our time for less than around £300 for a Golf sized vehicle, special deals aside. I wouldn't even do a protection detail for £50 (which is a thorough decontamination of the paint, a glaze/light refinement with a cleanser polish and a wax).
Here's a BMW 5 series GT that came through which was machine polished by BMW as part of the preperation...