I have spoken to a professional. He wants £150 per visit. He suggests once he has shot 1, the others will stay away for a day or 2, so he will want £150 per visit. He also says once we clear the present problem, more may come in the future. So it appears the cheaper solution is a gun. Also, there is no food & lots of deterrents, which they have just got used to.
Thanks for your advice I will check out a HW80