What are possible methods of interfacing with a button on a PCB?
Assuming the button travel is not too much, you should be able to find a hobby servo that can generate that much force at the end of a short arm within your power requirements. This has the added advantage of being very cheap and easy.

https://www.pololu.com/blog/16/electrical-characteristics-of-servos-and-introduction-to-the-servo-control-interface

If a hobby servo will not work for this because of geometry constraints, then a photo of the buttons configuration might get better answers.