Using Github and Netlify.

Create a free account on Github and create your website in HTML, CSS and/or JavaScript. Add those file to Github by committing those files and pushing it to Github.

Create a free Netlify account. Once those file are on Github you can connect your Github account to your Netlify account. Once it's connected it will automatically deploy it on a random url, but you can give a custom name. Your url will be: https://<your-custom-name>.netlify.app

Every time you make a change to the website and push it to Github, Netlify will put the changes online.

At this point you have zero costs.