Cancer diagnosis after surgery

Hello all - my almost 11 year old German shepherd/lab/chow mix was just diagnosed with cancer. He had a large mass on one of his anal glands that was just removed last week by a board certified surgeon. The biopsy came back with the official diagnosis of cancer that has a tendency to come back and metastasize. Of course they recommend seeing and oncologists and start chemo/radiation therapy right away.

They did several tests ahead of the surgery to try and rule out cancer and all came back saying that cancer was not likely however the actual tumor biopsy proved otherwise.

I know I can't afford the further treatments. I had to get a loan just to pay for the initial surgery and now I just have overwhelming guilt and heartache. Part of me wants to do everything to save my dog but reality is I can't go into financial ruin either. He is already a large breed senior dog. Even healthy he may not live another several years, but still.... he's my dog! I'm sure you all understand. I've already had a senior cat lost to cancer. In her situation it was too late and we only had a few months. But this is different. He just had everything (hopefully) removed by surgery.

So my question is for those that have had a similar situation, would you proceed with treatment? How much were the treatments? How does chemo and radiation affect the dog? I'd like him to have a good quality of life and not sick and dealing with treatments all the time, but of course doubt sets in and I ask what if? The closest place to treat him is about an hour away in major traffic we'd have to ride on each time. There is just a lot to consider. I don't know anything about cancer in dogs and the treatments so I wanted more info from people that actually lived through it with their senior pet before I make a final decision. Thank you all in advance.