I agree, a horse that age is not going to be around forever. If it were mine, I'd spend the $50 and watch the mass shrink. It could go away, it could just slow down. The other option is spending a fortune trying to conventionally resolve it. Or, risk spreading it with a biopsy. Most people have not even heard of clean horse, or blood root salve, let alone seen the results. I've seen a few cases first hand, and also heard amazing stories. For a horse that age, this the gentlest, yet most powerful method of management, in my opinion. I'm sure there are many who've never heard of this form of removal, nor seen the results I've seen, but will still dismiss it as a viable option.
You sound like me. I have managed barns for 40-50+ horses and the vet was almost never called except for coggins and rabies.
I'm not a vet person and will heal just about anything I can by myself. I've stapled horses back together and have grown legs back from bone.
However, I want to caution you about advising people against vets on this forum. Its a bit of a dangerous practice when someone posts a medical picture and you reply "Don't call a vet unless you want to waste money, do this instead".
Some things are easily fixed with home remedies and a confident, knowledgable horseman. People post pictures of injuries and illnesses and ask question because they are NOT knowledgable on the subject and need opinions on what they are dealing with, and if its serious enough for a vet visit.
To this, I usually give suggestions...and at the end, remind them that if they are unsure, it is always good to have a vet out for a professional opinion and one on one guidance. The last thing you want on your conscience is someone taking your advice on not calling a vet, treating the issue with the suggestion, doing it wrong (because they are unknowledable) or treating it wrong (since it was diagnosed just off of an internet picture), and making things worse.
I know you are eager to help and that's good. However, never recommend NOT calling a vet if the OP is concerned. You can share your experiences and you might not need a vet, but a lot of the people on this forum do.