If it moves to Amazon? Probably depends on the person and what they already have. Amazon hasn't charged more for Thursday night football (for example), so I'm guessing at least to start it will be more of a marketing add-on to get people to subscribe to Prime. So if you already have a subscription, I'd bet that it would be available for no additional fee.
Down the road, who knows. Apple TV has an extra subscription fee for MLS, so there's also precedent for streaming services to add surcharges for this kind of thing. But I think Amazon likely makes much of their money on Prime through the data tracking and being able to use data to have better targeting to promote their ad services so the goal in the short term is to continue maximizing that.
All conjecture of course.
