There’s a wide variety of viewers that meet Google’s cardboard quality standards out there. Simple and affordable, you may chose from any of these to dive into your VR worlds.
The official Google Cardboard is affordable and easy to use. Just a couple of folds and you are good to go.
Made of plastic, this viewer is priced a bit higher than other cardboard viewers. Yet, it is still affordable. It was especially designed for kids and promises magical experiences in VR.