Farmers don't pay anything unless they have problems specifically linked to squirells and want them killed, im not sure if you need to be a licensed pest controller though It's usually about a quid but my next door neighbour has been known to give me a crafty fiver for killing the little buggers. Just ask around. Theres more call for killing bunnies down my way so branch out a bit and just shoot what people want shooting.
Hope that helped. Aaron x

What is your main interest. hunting and fishing