Ok so there's a good chance I'm just being an idiot here, but I feel like a multiple worlds kind of interpretation serves well here. If, as you say, "the coin is deterministic, [and] in the overwhelming measure of the MWI worlds it gives the same outcome," then I don't believe the coin is fair. And if the coin isn't fair, then of course I'm not giving Omega any money. If, on the other hand, the coin is fair, and so I have reason to believe that in roughly half of the worlds the coin landed on the other side and Omega posed the opposite question, then by giving Omega the $100 I'm giving the me in those other worlds $1000 and I'm perfectly happy to do that.