I would just ask him how much did I owe him!
A fair price is relative. I would avoid any situation where there is any possibility that he could walk away thinking hard done by. If he says a price you think too high, just smile and pay it, in 6 months time you might find it was a fair price even though at the time it felt like you were being taken advantage of! Or if you discover you paid too much, never use him again!
If it was a neighbour and I knew him well enough, I would pay him £25 per hour for topping (1) and £1.50 a bale for (4), as he did (2) and (3) for his own benifit I wouldn't pay him for that.