What is the most effective way to use $200 in digital media?

1. First advice, stay away from buying email lists. They are very often inaccurate, outdated, and irrelevant. You want to really get people to explicitly consent to receive an email, and often double opt-in into your email subscription (look that up if you're not familiar)

2. The fastest way to get subscribers is a lead magnet. A good small e-book, notion template, checklist, or a manual collection of resources to help your audience do something. Check many of the top ProductHunt posts to see some examples. So I would recommend doing just that. Create good content as a lead magnet. Find a good hunter for product hunt, and go from there. You can easily get a few thousand subscribers from that one trick if your content makes it to the top voted.

3. So far, you haven't used your $200. You can use that to generate the content (pay someone to write it or do it). I'm afraid it's not enough budget for ads.

4. Try building in public (a common method for gaining traction these days).

Good luck! keep us posted on how things go.