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I'm not sure which one are you referring to, but you can usually see if the app, plugin or theme is free or paid.
In the Theme Store, you can find themes that can be added to your form, there are some paid and free themes, and I believe they are only one time payment.
You can find more details of a widget here, http://widgets.jotform.com/, I haven't seen widgets that charged users, although, it may depend on the author or the developer of that widget. I do see that there are Apps, http://apps.jotform.com/, that charged users depending on their used. These charges don't show up in your monthly subscription because you purchase them separately.
I hope this helps. Let us know if you need more information on this.