How do I purchase more than one plugin without upgrading?

I currently purchased a pop-over plugin a week or so ago and am currently paying $19/month for that plugin. (which I think is outrageous) From what I had read I could purchase that plugin and not have to continue to pay monthly.

Now I want to purchase another plug-in but not pay even MORE per month... but it will not let me purchase anything until I upgrade my membership to $40+ per month?! Is this for real? I can't just flat our purchase one plugin?

Please respond.