I think the business model is based on email subscribers. OP has mentioned elsewhere[1] here that he modeled the site and offering very closely based on Scott's Cheap Flights .com which was in the Cheap Flights domain.
See their story on IH. 320K / month in recurring revenue. https://www.indiehackers.com/interview/scotts-cheap-flights-...
[1] : https://news.ycombinator.com/item?id=16579003