We've heard that pathfinder is a pretty easy system to play with... Our experience with it supports that. To run a pathfinder campaign, you only need a single book. The core rulebook has everything you need for the basic stuff, whereas D&D 5e requires both the player handbook, the GM book and a bestiary.

You can download the pathfinder core rulebook (legally) free too, but its often easier to also have a papery version, as a 600+ page pdf can be slow to move about in.