SSL letsencrypt

Yep, I'm currently using it on about a dozen domain names and it's completely free... if you've got admin/root access to your server, it's usually as simple as going to https://certbot.eff.org/ and following the instructions according to your web server & OS... or if you're using the Plesk control panel, that page will point you in the right direction to install the Plesk extension. Even if you don't have admin access, some of the better web hosts will do it for you if you ask nicely.

Cheers, let me know how it goes