It's difficult isn't it, selling meat on means you don't have the option to DIY so you are a bit of a captive market. Have a similar scenario tho not as bad with my lamb butchery ATM, chose a butcher close to abbatoir and who could get the carcasses direct chilled but they want about 40% more to butcher them than the butchers we use where it's for our own use where we transport the carcasses to them with ice packs - and the other one does more work on the butchery too :-((
I do agree that butchers probably don't want the work so it's not like you can negotiate much, they will just say go away then. Which is their right, but if they do agree to do it I think the price should be a reasonable one for the work involved...which I'm not sure it is in these cases.
It's made worse by the ever shrinking number of abbatoirs as that means you are stuck with a more a more limited number of butchers if you want those on the abbatoirs delivery schedule.
I've decided that in future I won't mix own use and selling carcasses. Sale ones will go in one lot and be butchered costing €€ and for the others I will use the other butchers or do the butchery myself, I'm going to ask for butchery knives for Christmas!