https://merchantmoms.com/ssl-certificates.php is $75 annually and covers both www and non www (meaning https://www.yoursite.com and https://yoursite.com).
There is also the availability of a new one here which is $15.
That is called 'light' because while it does give the https and needed security; it doesn't provide the full verification to you as the site owner but to the server
Here is an example of https://merchantdads.com vs https://limerikeedesigns.com. When you view certificate you see the difference.