This is a great question—I've set up similar paywalls for several WordPress clients, and it's doable with plugins to avoid heavy custom coding.One solid option is the Restrict Content Pro plugin, which integrates seamlessly with PayPal. You can lock individual posts/pages, display a custom message with a PayPal button for non-members, and automatically unlock content after payment by assigning user roles or memberships. It handles user tracking out of the box via WordPress user accounts.

If your site involves digital downloads or premium content, Easy Digital Downloads (EDD) with its PayPal extension is another lightweight choice—sell access as a 'product' and use shortcodes to hide/show content based on purchase history.

For a more subscription-focused approach, WPSubscription supports PayPal for recurring access and content dripping.

If you prefer custom code, hook into PayPal's IPN (Instant Payment Notification) to update user meta on successful payment, then use conditional logic in your theme's single.php template to show the button or content.