As mentioned, it depends upon your location and available options. Some vets, like mine, don't charge to euthanize small pocket pets or injured wildlife. We don't normally see anything but dogs and cats in the hospital, but upon occasion, a client will have one of these pets as well and require our services at the end of it's life. The amount and cost of the solution is minimal and my vet considers it a courtesy considering the other options clients have to end the life of these pets. An adult snake may not be considered a pocket pet, and some vets may not have a clue about how to even euthanize it quickly (the solution can be administered into the abdomen, but it takes much longer for the pet to pass). As bad as it sounds, over the years, in addition to my time working at a wildlife rehab, injecting from the base of the skull directly into the brain works very rapidly. Finding a vein or the heart on some creatures, such as birds and turtles, is almost impossible.
As for the remains, if home burial is not an option, my vet, again, will not charge for these pocket pets. They simply get put with either the "surgical remains" or another pet for communal cremation. The crematory doesn't look in the cadaver bags to see an extra small body making the journey over the rainbow bridge with another pet. I think they are keeping each other company until it's time for them to greet their owners.
And if this isn't an option either, as bitsy said, a trip with the sanitation department to it's mass landfill/grave is fine. The pet isn't there anymore, just an empty body.
