That looks a very quick job with a light pole. I might be way off but i reckon i'd look at that as 3 hours hard work and would have quoted around £120 - £140.
And if it was simply algae on there i would hope for nearer 2 hours.
I would use a trolley and tfr or something for this. If you do alot of this work it would be worth spending £80 or whatever on a backpack and pump the mix up a pole 1st. Or put a T piece and shut off valves between pump and water tank and run the spare hose into a barrel of tfr mix.
And then connect the pole to the garden tap and rinse off.
I use a pump crop sprayer for conservatory roofs and lower and i would be interested to see how they would pump up that height. Cos mine has a maximum of around 12 feet. Horizontally.