right some people bug my happiness on this forum!!! and its not yourself for asking a sensible question.
If an estate asks you how much you want to control a fox problem then i would say a fair price is around £25 quid a fox and as you have said in your question there's no chance of any other sporting opportunities i.e. stalking , some fishing, or maybe even a day pheasant shooting then your quite right in charging them especially if they have came to you!
If on the other hand you had approached them asking about some fox shooting then fair enough you couldn't expect to charge them!
All my foxing ground i always get something back from it whether it be a bit of stalking or other shooting, you got to remember your covering a lot of ground burning fuel and all your equipment plus you have to bear in mind bullets aren't free whether your reloading or not!!
I can see some people reading this and thinking ohh i would do that for free imagine even asking that question maybe if they would read what is actually written in this question the estate has asked him how much?
In my experience these are the same idiots that come up my neck of the woods and offer silly money for stalking ground outbidding all the local lads by miles then takeing on inexperienced stalkers to fund the lease who are willing to pay through the nose as they havent any other ground! however this is a thread for another day!
so in relation to your question i would say £25 a fox!
Listen carefully and you'll hear the sound of a nail being hit on the head