Call Light St and find out the price. Dr. T's prices are very reasonable. I would also suggest calling BARCS and see if they can help you. They have much nicer people there than they used to have.
Take him to light street animal clinic. They'll know what to do or you can call them. I can not answer this for you. I'm sorry your rat is sick.
I do not know honestly. You could call the vet and just ask... call an Animal Hospital as they are likely to get a greater diversity of pets - or you could also call University of Maryland or Johns Hopkins University and ask who oversees euthanization of research animals. Or call the National Humane Socielty. All of them I think should be willing to assist you.
Thanks! Your answer is awaiting moderation.