The plugin is 100% free for users, Payment Plugins is able to offer you the plugin for free because we are a verified and trusted Stripe partner and we are paid to support the plugin with excellent code.
You must create a stripe account in order to accept payments through the plugin. Customers, however, do not need a Stripe account in order to make payments. They can pay via credit cards, Google Pay, Apple Pay, and even local methods like P24, iDEAL, Konbinin, PayNow, and BLIK.