HTTPS has been a tiny bit of Google's ranking every since 2014 and as of April of last year, they are still saying that isn't in the plans to change the weight of that element. (source)
What has changed that you need to be aware of is the browsers. Both Chrome and Firefox have announced that upcoming versions will start highlighting sites that are not using the HTTPS protocol. Even if you do not need it with a static or information only sites, this is already the case in the most recent versions of both browsers on pages that require login such as WordPress admin. The top one below is Chrome and the bottom one is Firefox. Chrome is supposed to show this for any nonsecure website page in July. Firefox is not going that far but will start that process with the next version as well.
How the visitors will react to this is pretty much anyone's guesswork. If someone is just looking for info, will that influence where they look? We've all been trained to look for the padlock when logging in or making a purchase. Who looks at that bar if they are just browsing?
Fortunately switching your site to HTTPS is not hard if you have WordPress. You can make that change in the general settings by just adding that little 's' in. Zen Cart requires changes to the configuration files which is a little harder. But it does take more than that to have your full site automated to HTTPS only. It's not hard to do if you have cPanel hosting (redirects) but this facility on other servers may take actually writing the file yourself. Some hosts may not even allow the file code (.htaccess) to work. I know this was true only a few years ago. The truth is that you will probably need help putting this into place.
The question then becomes is it worth paying for? First, contact your hosting company and see what assistance they will provide. If that fails, then I'm not sure the answer is to spend your money. Google is not changing their algorithm – only the browsers are adding in more notification about secure websites. Will that impact your visitors? The answer is just not available yet. It's not mandatory now but will become more important in the future.
I do recommend keeping this in mind if you have something else done on your website that you do have to pay for. See if you can't get your web pro to set this up for you during the next time you do have to put out some money.