[Taliesin]

Advice please, our local farmer has done some work for us and I'm trying to price up for a fair exchange. Work comprises (1) topping a two acre field and leaving grass to return to ground. (2) cutting grass on 2.5 acres field, gathering the grass. (3) making 15 large round bales which he has taken for feeding his cattle. (4) baling 35 small bales for our use here on the smallholding. Thanks in advance.

[bj_cardiff]

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.

[arobwk]

Taliesin, hopefully someone here will be able to help with the equation (edit - I see bj_cardiff just did).

I do not wish to appear critical, but would have been best to query balance of costs/favours before the event/s.  Why not just have a chat with the farmer? 
I'm going to guess, given that he has not mentioned money so far, that he will probably say "that's quits" - for now at least. 

[Backinwellies]

Topping … £20/hr here in Wales    probably bit more in S E Eng.

[SallyintNorth]

Man and machine £30/hour hereabouts.  Baling 50p / bale (small bale).

[twizzel]

Small bales 65p per bale, mowing about £12 an acre, turning grass and rowing up £30/hour. Just ask him for an invoice and expect to pay vat on top of the prices mentioned.