The cost of van insurance will vary greatly depending upon personal circumstances, value of vehicle, area, etc, etc.
As for buying a van mount and a trolley, don't bother with both, if you can afford a van mount system with 100m or more of hose, you will never need to use the trolley. I sold our trolley system last year on ebay because it was redundant.
Believe me it is so much easier and quicker just running out a hose and pole from the van to the job, rather than humping a trolley pack complete with pump and battery pack plus 25-50ltrs of water and the pole!