Prozac is a cheap answer to many cats with anxiety issues. There may be some natural herbs that you can try without a vet visit. A thread about that in cat health might get you some good ideas.I understand your distaste at the thought of putting down an animal that is not clearly suffering. I have put down the two dogs I grew up with due to cancer and hip dysplasia in their old age. I have also watched another beloved family dog die slowly and painfully in front of my eyes due the inability of my mother to let her go. I do not mean to lessen or insult those situations which euthanasia is used to end physical suffering.
I am trying to find the best scenario for my cat at this current time. That does not necessarily mean euthanasia. I am simply trying to create a soundboard for ideas. I do not have the money for her vet bills if her odd behavioral issues are due to an underlying neurological problem. No, I did not think of the possible financial burden when I first brought her home when I was 12 years old. I know that is my own shortcoming. However, at this time she is living a life in constant anxiety and her behavioral patterns have worsened. I do not wish to keep her in a household where she lives this way, and the same problem arises if I try to find a home for the other older cat. Both are old and unlikely to be adopted. I am just facing the reality that I cannot find her a home on my own and surrendering her to a shelter, merely for her to be traumatized before she is deemed "unadoptable" by the shelter and then euthanized, is lengthening the same end.
12 year olds are not expected to think about the future vet care costs of pets. That's why it's called childhood.