I've got no real knowledge of prices but would say:
4 acres is more trouble than it's worth for a lot of people and many would work on a barter system such as exchanging a small amount of hay for hedge cutting later in the year..
Is the land flat, has it been top dressed, has it been rolled (broken blades cost time and money)?
Of course if you don't get it sorted in the next few days (should this weather break) it will be worth nothing with the whole country making fine hay at present. It may then be a case of what will it cost me to get my field tidied up?
Personally I'd see if I could get a few quid more and say 'thank you very much'.
Just my 2p