[vessenes]

I both understand the demand for this and dislike it. But, assuming ethical questions stand aside, I do have some pricing reactions:

This should be a monthly service, full stop. You mention users use it once, and then not for a while. That is the best possible scenario for a recurring revenue business. You should stop offering one-off purchases immediately if you want to see revenue grow.

I can think off the top of my head of a few 'ongoing' value adds you could do; in particular, you could remember emails you couldn't find, and if you do find them notify the user. There are probably more things you could imagine if you were closer to the business.

This would also let you charge spammers a lot, or preferably just keep them out and stay more moral by just capping the monthly requests at something reasonable for a human, not a spammer.

[mark242]

"This would also let you charge spammers a lot" should be rewritten to "This would also let you charge unwitting victims of credit card theft a lot, and get a ton of chargebacks".

[Spivak]

That seems to be true of any business that accepts credit cards.

[CodeWriter23]

As a user of external services to build my own SaaS, I am actually forced to prefer the per-use billing model. So much so that I have signed up for only 1 service that bills monthly (and because they are priced way below the competition's monthly charge), and 4 that have a usage-based billing model.

What the usage-based pricing model does, it helps you capture startup customers early on when they are pre-revenue, then you get to keep them as they grow.