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.