Niche sites I have had in the past have included a photography equipment site for urban explorers (one of my main hobbies).

The site contained some affiliate links but it also generated income through display ads and the occasional sponsored post.

Driving traffic, as you noted is key to most of these things.

Social media is probably the lower cost and most straightforward method.

And I did use social media (IG was what worked for my store). If I were doing it again today I’d strongly consider Pinterest as I have friends who have made a lot through that.

Besides social media, and paid advertising, creating original content is really the best solution. It is slow going but Google heavily rewards unique content.

A shocking small amount of content on a subject of any size is actually original, insightful, and well organized.