If you do a redirect from HTTPS to HTTP nobody (search engines or visitors) will be able to access the HTTPS site, which makes paying for having an SSL certificate rather moot. In this case all you need is to disable HTTPS on your site (Force SSL -> None in Global Configuration) and set up the non-www to www redirection in .htaccess Maker.
IMHO it would be FAR better to go the entirely opposite way: set Force SSL to Both in Joomla's Global Configuration and set up the non-www to www redirection in .htaccess Maker. Moreover enable the HSTS Header option in .htaccess Maker to force all browsers to use the HTTPS version of your site. This way search engines will only index the HTTPS version of the site. It absolutely makes no sense whatsoever to not do that. HTTPS adds a measly 1% to your server load (about 0.03 seconds increase in page load time – one fourth of the time it takes you to blink really fast) and vastly increases the security of your visitors' data.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!