The humane socity offers this service in an injection. All vets do too, but they can cost $300 to do it. I would think that because the humane society is non-profit, they would be less expensive.
I am going to get my cats cremated and put with me and my husband when we are cremated. Maybe the cremation place could recommend a caring vet who will come to the house and do it.
Either way, we all will be crying with you.