COlady, I'm sorry to hear the news about your dog, but it's very promising that the vet thinks that he could do well with chemo. Several years ago, I was in a very similar position (with a dog of similar age) and, after much consideration about my dog's temperament and consultation regarding his quality of life during and after treatment, made the decision to try chemo. Fortunately, it worked very well, and he lived for another 2+ years. He handled the chemo process - and all of the visits to vets, side effects of chemo, etc. - like a champ. As is true with humans, some of the drugs in the chemo rotation caused more side effects than others, so we had some "down" weeks here and there, but most of the time, he was happy, went on walks, ate lots of good food, played with his toys, and did all of the other things that he loved (and that we loved about him). I monitored his mood carefully throughout the chemo treatment and would not have hesitated to pause it if I'd felt that the quality of life tradeoffs were not worthwhile.
Even many years later, I miss him very much, but it's a great relief to know that I did everything I could to help him have a good - and longer - life, and having those extra 2 years together was priceless. (Strange as it sounds, I even look back kind of fondly on some aspects of the chemo experience - driving in the car with him by my side, keeping track of his medications and appointments, making special meals for him, cuddling together, watching him get healthy and feel good again.)
Many people don't see the point in spending that kind of money on a dog, even if they can afford it. I understand that that's a common point of view, but I happen to disagree, and this is a highly personal decision. My dog was a beloved family member. Under similar circumstances, and knowing what I know now having gone through the experience, I'd do it again in a heartbeat.