There was a thread on here not long ago about vet costs, including neutering, spaying, vaccinations. (can't find it I'm afraid)
I will be paying around £50 for Otis to be neutered. Though vets vary from £30 (my last vet) to £80 in my area. Ring around and ask for some quotes, plus some vets vary the price depending on age and breed/size. So bear that in mind.