VERY much so - always ask first.
If people need to pay to use the site then you will need an extended license so thousands of $ not $59.
WordPress is great but you might want to be cautious when it comes to trying to do something like this on the cheap or cut corners when there will be a lot payments and confidential personal information.
The level of security, encryption and so on would normally be way above what any stock theme (irrelevant of the payment portal being used) can provide, and even if you find a theme with membership you will almost certainly have a huge amount of customization to do to manage profiles, bets, payments, profiles etc.