I guess I agree with the majority. Once you adopt a pet (or it adopts you) and you make the decision to include this living being into your "family" then they become just that - family. Having already gone down this road with my Little Bear, who was a Russian Blue that lived for 18 years. He became ill, first with Lupus and then developed Diabetes a year later, from the steroids used to treat the Lupus.
At first he needed to go to the vet every week for a shot of steroids which made him feel great for about 5 days. Then he would start to wane and would need to go back to get another shot. At $50 a pop and me being on disability, I just could not afford it. Luckily, me entire family used the same vet and over the years not only spent a fortune combined, but also developed friendships with the staff.
When I broke down there one day, and told them that I couldn't afford the treatments but that I couldn't stand the idea of no more Little Bear, they took pity on me. They sold me the injection med and gave me syringes and needles so I could treat LB at home. They told me that they had NEVER done this for anyone before but taking our past into consideration, they accommodated me at every turn. It helps when you have a good relationship with the vet.
I suppose I would go without some things if it meant my pet would be better off; even if it was only a chance. And though 3 of our pets are adoptees, 1 was a purchased pedigree (the Abyssinian - Amun). And even though I never in my wildest dream thought I would ever spend $750 buying a cat, I did just that because I fell in love with him. And it was the best decision ever. So, once I found out that he has herpes which is manifested as upper respiratory problems in felines, I have already spent money on treatment and once he is over his slight flare up, I intend to have him vaccinated for $104 so as to reduce his outbreaks.
But there would naturally be a limit when it comes to finances as there is only so much money and then nothing to fall back on.
So, in agreement with most, it would depend. I hope I don't have to face this anytime soon. And I hope Rojo isn't having to struggle with this type of decision.
Rereading Robin's statement, if the pet would most likely have a good quality life, I would probably do whatever I had to in order to pay for treatment. Even (God forbade) going back to work in order to have the money.