Heads Up Display Helmet With arduino
There is a fairly inexpensive solution, but it's not Arduino based.

All you need is:


the Google Cardboard sdk
a fairly modern and powerful Android phone (I have a OnePlusOne and it works well with Cardboard apps) - assuming you already own something similar, this is where the big saving happens :-)
a compatible head unit: there are many available on ebay (on some you might have to drill a hole where the camera of the phone is located.) price got from about $5 to $25
some high level programming skills to write your augmented reality application, but there's no way around it :-) - you might even find some demo on the net.


Here the basic of the solution I'm proposing is to take the video stream from the front camera on the phone, use the CardBoard API to create a view for each eye (yes, you will loose stereoscopy, since each eye will see the same image from the camera) and overlay it with whatever info you would like to show. The simpler case could be a compass, where you show N-W-S-E at the top of the field of view. Or you could even add a map, like in a FPS :-) 

The part where the arduino might come useful is if you want to create some (bluetooth, for example) sensor and/or controller (using the usb port from the phone requires both a phone with HW that supports host mode and a rooted device).