trolley system ready made barells ro/di pole with brush about a grand bit less from some suppliers, van system inc all the bits a little bit more. be aware how much weight can be carried in your van... one litre = one kilo so 300 ltrs = 300 kilo.
if your van will take say 500 kilo this includes all the kit tank water pole etc and you any passengers etc. check insurance co make sure they are happy you are carrying lots of water, some are not happy!
going the diy route will save you quite alot of beer tokens.. horses for courses really are you the type who wants to drive in to a supplier and drive out with it all fitted tested gauranteed and shown how to use?
going the diy route can be sort of fun but you will know alot more about the system but it will take you some time to get it right. would you consider waterproofing the floor incase of a spillage? lots of things to consider... will you keep trad kit in there as well ladder on top of van maybe? all adds to weight.
you can cut costs a bit and buy some bits off this site from other window cleaners or ebay but ask the good people from this site before you buy!!
good luck with your quest it will take a bit of time to sort out but keep commiing back here and ask more questions.
i would say start with a budget maybe a grand and see what you can get for your money.
