I'm pretty sure Unreal Engine mobile isn't being used for $.99 apps, unless they are essentially "free to play" games with some sort of built in credit system (so in actuality; pay as you go) or built in ads actually generate enough revenue to pay for licensing the engine in addition to covering production costs.
Keep in mind that the main purpose for licensed game engines is to facilitate ease of development rather than to simply make the most visually impressive title possible.
One of the biggest advantages the mobile market has is due in part to the lack of physical media/inventory and partly because licensing fees are based on a percentage rather than a flat rate as they are on consoles, is scalability when it comes to pricing.
Yes, free and $.99 games are the most common, but as games continue to increase in production value (outside of the realm of developed by one guy on his laptop or a few guys working out of a garage), publishers are charging more for what could easily pass as a $30 mobile game on a dedicated handheld, yet rarely do they ever cost more than $20. $10-15 seems to be the range for full titles like Final Fantasy IV.
I would imagine most games being developed with Unreal Engine would fall into the same category unless it relied heavily upon ad subsidies or a pay as you play system.
