Ask HN: How to monetize small web apps

I recently made a web app that is gaining quite some traction in it's community. Imagine it as a single-page web-game. It's currently sitting at 1k unique daily users and I would like to try and monetize somehow.

I would add some small un-intrusive ad(even tho i'd prefer another solution) but it's not a content website and both media.net and adsense said it's no go.

There is also not much to convert it into a SaaS. It's whole appeal is that it's something easy.

I have also other similar apps of varying degrees of success and I could possibly apply the same.

Any other ideas of what I could try that is not exploitative of the users?