Oh no, I'm so sorry about Skritch's ear tumor.
I don't have any experience with the surgery, but the cost range you cited wouldn't surprise me. If you decide to go ahead with it, I hope it'll be done by a very experienced specialist.
What was the vet's recommendation and prognosis with and without the surgery?
I haven't personally used CBD oils, but I know several people who find them pretty effective for their kitties, though maybe not as effective as a med like buprenorphine.
The great thing is that she's doing well right now, and hopefully that'll continue for a long time!