In my experience in software as a service it is better to just charge from the beginning. Now, I do have a free offer, but only LATER when the concept is proven, the marketing is refined AND I want to prevent anyone from undercutting me – how can you undercut FREE 🙂 ?

You could of course combine the two concepts and just start accumulating leads for them.

Then contact them however you want (beware of gatekeepers) and show them your screenshot of all the leads you have for them, offer a limited number of the leads to them as a “sample” and IF any of the leads prove profitable to them, then make an agreement to start charging.