Don't know if this helps
As you have seen by these posts, we have all been thru some similar things. When I first read the nose bleed post by pupppwr I could see the exact same symptoms in my dog.
I think you need to get the vet to look inside his nose to see if there is something up there. If it is bleeding from one side only, then definately it could be a similar case. I have been told that this cancer is more common in the larger breeds.
I would not want my dog to be in any pain whatsoever. I also would not want to put her down if she still could get over it and have a little longer to live.
I had the Rhinoscopy done and a biopsy of what was there, it cost about $1k. But I think having that done actually helped her a little, because since then she has not had a nose bleed, namely because I have her on an anti-inflamatory and painkillers every day. SOmehow I think this is helping.
Prior to the Nose bleed issue I was told that she had a tumour in her parathyroid, and spent $5K on that operation to find absolutely nothing there.
The nose bleeds then started after that operation and progressivley became worse as you no doubt have read the other posts here.
If this is a similar pattern with you, i highly reccomend going for the second opinion and see if its the nose.
PS, my dog is also loosing her sight, but i think thats due to cattaracs, don't know if its related to the cancer.
Hope this helps.