There are several non-profit certificate authorities out there now that provide with free SSL/TLS certificates. On of them is Let’s Encrypt. I recently moved from HTTP to HTTPS using THIS that basically uses Let’s Encrypt’s certificate authority to issue free certificates.
You will need to edit your Nginx/Apache configuration files later on and also add a CNAME for the CAA etc. but it’s all worth it! After all, you get FREE HTTPS! 🙂