You don't have to come across like a sleazy porn slinger by using a call to action button on your site (without scrolling).
Making it frustrating to find the main thing you want people to do is certainly unwise.
At the absolute very very least, you should attempt to approve or disprove your theory by doing A/B tests. A being your current design, and B being your current design + a large easy to see join button on every page. (top right corner imho).
I think you'll find you make more money with B.
You could do this easily with a third party solution like Optimizely (
https://www.optimizely.com/ab-testing) and I'm sure there's many more.
Also, I see that as a free user I can see the size of the files and attempt to download them, but the download button doesn't function. This is a great opportunity to remind people that you're a membership based paysite that relies on its users to buy memberships. A little unobtrusive pop-up button could appear once per session when people click that download button, and provide a link to your join form. Without it, people aren't sure if your site is just broken or what. They may not understand your business model at that point. It just feels like it doesn't work. So that's bad user experience just as much as hitting them with a little popup is. Popup is a dirty word, it's just a little notification, could be very small on one line of text.