First off, if you are treating your snakes in a way you would consider "not exactly humane" you shouldn't have them... If you're meeting their needs then that's humane.
Many people on here treat their snakes as pets and are willing to spend what is needed to care for them. Yes there is a scale of necessity, and in this case it seems like the best option for both owner and snake may end up being euthanasia (or it may not, I don't know). There's no reason the OP should feel bad about wanting to spend money on his snake whether it's worth $50 or $500. I personally take responsibility for any pet of mine and what determines whether or not they get a vet procedure isn't their 'worth' it's the cost of the procedure against how likely the procedure is to work and how much pain and stress it will cause them.