I never had pets until I met my wife, but now we have four cats. She grew up with dogs, and said that her golden retrievers all passed from various forms of cancers (I think every time one passed her parents got another one, or had the new puppy in the house as the elder one was deteriorating...she said it did allow for some transition). But she wanted me to tell you that they DO NOT ALWAYS/NECESSARILY exhibit ANY signs or symptoms that they are in pain; they may still seem content around the family, going for a little stroll, eating etc., but they could be suffering tremendously and just putting on a brave face. Many animals are like this.
One of her goldens started limping after what they assumed was a little slip on the ice in the yard. Gave her some pain killers wrapped in a cheese slice for a few days. Limping got worse, but the dog was otherwise fine - eating, walking up and down the stairs to the kids' rooms in the basement, generally SEEMED content. After a few days they took her to the vet. Her entire leg bone had disintegrated from the cancer that had been eating it, that they didn't even know she had. Had to put her down that night.
Not trying to put any undue pressure or guilt on you, and of course you will know when the time is right, but just keep in mind that your pup might be a trooper, more than you think.
As for the moneys, I've never been in the situation where I've had to shell it out to keep an animal going, but now that I'm attached to these cats, I don't know where I'd draw the line.
