My absolute favorite -- I carry it with me everywhere to show off VR is the $22 Goggle Tech: http://www.amazon.com/Virtual-Goggle-Tech-C1-Glass-Smartphones/dp/B00SVG8VSS/ref=sr_1_1?ie=UTF8&qid=1446914214&sr=8-1&keywords=goggle+tech

It's open-sided so you can just tap on the screen to open or switch apps (instead of having to get the phone in and out of the headset) and you can look over people's shoulders as you show off VR to them. You do have to hold it in front of your face, so this is NOT the headset you'd use for long games or watching movies -- it's for either quick apps or for showing off to friends.

And not quite $35, but this Ling VR is now on sale on AliExpress for $47: http://www.aliexpress.com/item/In-stock-Lingjing-xiaobai-360-degreen-immersive-VR-virtual-reality-PHONE-3D-glasses/32434907562.html?spm=2114.01020208.3.34.BtULhG&ws_ab_test=searchweb201556_2_79_78_77_91_80,searchweb201644_5,searchweb201560_9

It's my favorite of all the Cardboard-compatible enclosed headsets. Lenses adjust two ways, and it comes with a very nice free Bluetooth remote controller (instead of a button). Very lightweight, comfortable and a very nice wide field of view. I like it better than the Firefly, which doesn't let you adjust the lenses.