Side project evaluation

A couple of years ago I've launched an Android app that is currently generating an income of nearly 250USD monthly. The source of income is in app ads of single ad provider (AdMob).

The app required nearly zero maintenance as only one fix was made since it's launch, and is the leading app on its niche. I'm thinking about selling it to fund other projects, but I'm having a hard time on putting a price tag on it. Any strategy or ideas on how to do this ?

Some interesting metrics about it:

Around 18k installs on active devices
- 10% growth on last month
- 22% gowth on last trimester
- 53% growth on last semester
- 220% growth on last year

Average of 4000 DAU (measured on Fabric)

Advertising Network stats:
Last month:
- 2M total impressions
- 0.28% impression CTR
- 5500 clicks
- 0.14USD impression RPM

Last trimester:
- 5M total impressions
- 0,30% impression CTR
- 15000 clicks
- 0.14USD impression RPM