What would you do for you canine best friend?

[Blueface]

I have being going through a bit of a tough time with my Maltese Champ.
He is 13 years old and fondly known as the "grumpy old man".
He lives to put his body as close to yours as he can for warmth.

A few weeks ago, the groomer called me to tell me she was concerned with a large lump on his side. I ran to pick him up and immediately took him to the vet. Just five days later, he was operated to remove a rather large mast cell tumor. They are rated from a 1 being benign, to a 3 being the worse case. His was a 2. Unfortunately, the cells extend beyond the extra tissue they took out. So basically, Champ has the cancerous tumor cells in him and likely to recur within 3 to 6 months.

It was recommend I see an Oncologist, which I just did. Basically, after a couple of thousand dollars in the surgery, a few hundred for x-rays post op, I now need to spend another $1,000 in additional tests to see if it has spread or is contained.

If contained, radiation is recommended to the tune of $4,000 which gives him a 95% chance of no recurrence between 1 and 3 years.
If spread, needs chemo, which costs nearly as much, and only has a 50/50 chance of survival/no recurrence at the one year point.

So, not like I can dig up this kind of money overnight. I need to take out some loans and will if I have to. I feel it is nuts to spend this kind of money to try to save him and perhaps not really improve his life but instead make it worse along the way.
On the other hand, he is truly my friend. May sound nuts but I consider him no different than if posed with this issue with a child or family member. I feel I won't be able to rest in peace knowing I didn't give my friend a fighting chance and help him out by doing everything possible. However, his age concerns me. He is 13. He is no spring chicken anymore.

I have an appointment tomorrow with a very renown holistic vet. Let's see his perspective and then it will be decision time.

Any opinion welcome. I am sure in the end, I will be as confused as I am now but at least I will know how others feel about the same issue.