This will vary depending on what sex and type of animal you are responsible for, and to some extent between vets. It’s something you should discuss with your veterinary surgeon, ideally before you bring a companion into your home. Some charities and vets can offer subsidised or discounted neutering schemes if you are eligible.
However, one should equally well ask:
How much will NOT neutering cost?
Bringing up a litter of puppies or kittens is an expensive business – in many cases the costs of feeding these extra mouths alone will be higher than the cost of neutering. Furthermore, if there are any complications with either pregnancy, birth or with the puppies or kittens afterwards, the veterinary costs can be very substantial indeed.