MemberStack charges a flat transaction fee of 10% on the Startup plan and 3% on the Pro plan, and 1% on the Scale plan. Stripe charges an additional credit card processing fee that depends on a few different factors. See Stripe's pricing for more details.
We’re working on a content management system that would make it possible to store anything securely on any website. Although, it’ll be a few months before something like this is ready (01/2019). Until then, MemberStack protects pages and content on those pages using redirects. They can't be "turned off" from a browser, but there are ways to access the HTML of a page if you know what you're looking for, and what you're doing. Therefor, we don't recommend using MemberStack to protect highly sensitive information.
Pre-revenue companies, students, and other folks who can't (yet) afford the $25/mo fee. We've been there, so we're happy to work with you.