Userbase is the easiest way to add user accounts and data persistence to your static site. No backend necessary. Up to this point, I’ve almost exclusively listed products and services with a free tier. However, cheap doesn’t always mean free. Technically speaking, Userbase is open-source, so you could run your own version for the cost of hosting it somewhere, but they also offer a hosted version for just $50/year (for now). The best part of that is you aren’t limited to a single site or applications. That price gets you unlimited apps and unlimited users.