Greetings! Infinity Runners are one of our favorite types of game here at Voorhees. Making something like Subway Surfers or Temple Run would be a great pleasure for us. Integrating the app with Facebook or ads should not be a problem too! About engine, we prefer to work with UE4 here, but we have 4 years of experience working with Unity 3D, so that's not a problem at all.
Please let us know about further details! We don't like to rush projects, so we are going with 30 days of development to make sure you get what you're expecting.
Kind regards,
Voorhees Team