PDF's are totally free. You also can get the books at print cost. I would recomend [](drivethrurpg.com) it is kinda the hub for buying RPG's.
Follow the links. Click at your own risk
https://www.drivethrurpg.com/en/product/500476/cairn-player-s-guide-2nd-edition
https://www.drivethrurpg.com/en/product/500478/cairn-warden-s-guide-2nd-edition
[Creator's site](https://cairnrpg.com)

There is also the [first edition](https://cairnrpg.com/first-edition/). It is smaller and faster to start playing