This is 100% dependent on the type of extension you're building out. Without knowing more about the nature of the extension, it is extremely difficult to recomm

This is 100% dependent on the type of extension you're building out. Without knowing more about the nature of the extension, it is extremely difficult to recommend a proper monetization model. Who are the target audience? Is there a built-in model you can leverage? Too many unknowns to recommend anything valid. It's like asking how to monetize a website. General advice won't help much...