Yes, I agree with you, they have a die hard fans and Logan Paul has a big number of followers in his youtube channel.
22.7 million as of the moment, I don't know if it has increase because of this fight, but it's a big number even if 10% of that will buy the PPV.
KSI vs. Logan Paul match generated around 1.3 million PPV buys, which was very impressive for a boxing match between two amateurs. Since Mayweather is involved, we can expect that number to increase by manifold for this match. But while the KSI vs. Logan Paul had a price tag of £9.95 per PPV buy, I expect this match to be more expensive. So at least some of the fans are going to find it unaffordable.
It is not that is unaffordable if somehow they decide to make it more expensive, it is a matter of simply not being worth your money, while that price is cheap I can think of at least 5 ways to spend that kind of money and get way more entertainment than the hour that I could get from watching an amateur fighter and a Floyd Mayweather that is not serious at all about this fight, so while a boxing fan could watch it just because I have no intention to do so if the price is too high.