As a vet student, this is a big deal for me both professionally and personally. And when it comes down to it, there is no one that can make your choice for you. That being said, it is hard for us as veterinarians (or up to this point for me, as a vet tech) to counsel you as owners. However, I would greatly encourage you to consult your vet when you have doubts. We as vets have nothing in mind more than your pet's well-being and happiness. We are taught to evaluate the quality of life for your pets.
That said, pay attention to your pet. They can tell you when it is no longer worth it for them. Please don't keep them alive for you. I became aware of a horse being kept alive (downed) for weeks, to the point where he developed bed sores, even when the vet told the owner that it was very very unlikely that they would be able to get the horse back on his feet. He was ready to go. So listen to the subtle cues that your pet, and your vet, are giving you. We can help you make the decision. Vets are also good resources for grief counseling, etc.
Money, money is tough. Ask about resources for help with payment (it's out there!).
Last edited by potterspoet; 09-25-2010 at 12:10 AM.