I think its wrong to look at the cost for muck on a individual crop/ year basis.
If you apply a single dose to one crop and put all the costs assosiated with the muck to that crop then its a non starter but if you have a long term view that muck is going to become a long term integral part of you farm and you can see beyond just the ££££ then it works.
If you say the muck costs £60 acre for example, applied once ever three years through the rotation then thats £20 year/acre. I dont know of anything else i could spend that money on which will do as much good long term.
Theres far more to muck than just nutrients and OM, regardless of soil type/location/farming policy it will make any land better.
I agree with all of that. So, what £ value do you put on it?