i am not sure if you are having a joke glyn
but just incase
tank = 25 L barrel
the pump and battery will be in the boxs
Window cleaning pump either flojet or shurflo approx £85.00 - £120.00
33 amp hour battery approx £45.00 - £55.00
sack truck lets say £35.00
bit of welding are you suggesting using a professional firm? in which case I cannot see them doing anything under £30.00
pump box £20.00
battery box £20.00
waterproof On/off switch £4.00
Battery connection terminals £5.00
heavy cable let's say £4.00
Using the lowest price pumps and battery this would be £248.00
And on top of that you will also require a battery charger - minimum cost approx £20.00
then lets look at how much time it takes you to construct it or are you not going to consider any labour charge for loss of earnings during the working day?
If its a hobby then you dont need to price for labour, but if you are making it during a working day then you must price in the loss of income at say £30.00 - £40.00 an hour