Mike,
When you say connect to the customers outside tap I’m guessing you know you need a tank to fill as the water pressure from a tap wouldn't be enough. I connect to customer’s water when I get there; however, if they have a problem with that I bring it with me. I've only had one guy complain about me using his water and I told him I would have charged more if I’d brought my own - I wouldn't I just didn't like his tone and I did a survey and he was happy at me using his.
Anyway, I think you should be looking around £3500 for a good setup. I would think you'd have a pressure washer (3600psi), hot box which transforms cold to hot (deal we any stain), a wet/dry vacuum, and 20metres of cable. You could maybe do it a lot cheaper, however, make sure you buy the right equipment to tackle any job because they do come up.
I’m not to sure where you based but if you’d like to come out with me one day feel free.
Alex