You'll find when you do domestics, you end up using the same brushes or trying the same no matter what system you have. As long as the water is pure and you know what your doing its the same. I prefered to keep the money in the pocket. Think about it all you need is _ Filter, tank, pump, battery, hose, pole, brush. Would you pay thousands for that? Remember, your customers don't know the difference and when your doing windows only the pole and brush really matter. 2000 will buy you a bling DIY. 1000 will buy you a really decent domenstic one. Buy a ready made one and like you said thousands.
I have the ionics brochure, the difference between a five hundred litre tank and an 800 litre tank is like a grand. Thing is you may only get a slightly bigger filter and tank. RIP OFF. And most people think there brushes are crap. (of course, some like them, but taht's it, you'll end up trying loads of different brushes) DIY DIY DIY