I made a service called Amazing Airfare (
http://www.amazingairfare.net). I'd email and text people curated, ridiculous deals on airfare (50% off or more intentional flights from USA/Canada).
I wrote a good medium post (https://medium.com/@zacharycohn/on-mvps-glueing-things-toget...) about the process of building it.
I grew it to a couple hundred paying subscribers ($8/m) (which was about 93% profit), then sold it to an acquaintance when some life situations changed. I get paid out an amount per month according to our agreement.