I would buy a used van and fit my own system.
Not only can you fix it, when it goes wrong, or something leaks, or when the water stops flowing (which it will on occasions)
but you can also 'tweak' it to how you want to work.
I used to work out the back of the van, so that's how my system was set up, but then I decided to work out the side of the van (which I now prefer) so I had to rejig the whole setup.
Never believe people when they hint that they might want a window cleaner; some do but some don't.
I have given out loads of leaflets to people who said they were 'interested' and never got a call back.