Fees are low at the moment yes, but that can change in a moments notice.
Let me look around to see if there's a safe way to bet with LN. It should be possible with hold invoices, its just they don't usually hold for that long.
We can do this on-chain since the fees are pretty low right now. I was thinking of a simple 2/3 contract. If there's a disagreement between the bettors, the judge will decide. nostr:npub1qny3tkh0acurzla8x3zy4nhrjz5zd8l9sy9jys09umwng00manysew95gx could be the judge; I like him, and I discovered Nostr through him. If you agree and he accepts, it could work.
Discussion
Yes, fees might increase in the future (they're likely to go up), but that's the cost; it's part of the protocol.