Posting answers to highly targeted Quora questions is free. Launching on Product Hunt is free. Writing targeted content that ranks on Google takes time, but costs no money. Retargeting ads are cheap.

I agree that if you're trying to build a big business, you need to think hard about how you're going to get customers. But if you're just trying to make a couple hundred a month (as OP asked), it's a completely different ballgame. You just need a tiny sliver of an enormous pie.