I've just hit this myself. It's simple. I've just installed the extension and played around with it. I then hit a shortcut and got told about the paid version. I've only tried it for a few minutes. I like it but I'm not going to buy it yet until I'm convinced it'll really help me. Still, I'd like to know how much it is before I click on the button "Buy Paid Mode License Key". Most users will not click on this unless there is a price. Words are very important. As August points out, if you change the wording to something like he mentions or "view price for your region" or price is between x and y depending on your country people can help decide without jumping through hoops.

Regardless it seems like a decent extension and if it proves useful I'll certainly compensate the developer being one myself.

All the best.