Has anyone tried building an INS-like system themselves ?
Sparkfun makes nice little "9 degrees-of-freedom" kits. I've managed to get one working on a stripped-down Raspberry Pi (ODROID-W) logging at 600 Hz currently to a SQLite database on an SD card. I figure I could log from an array of three, six or nine sensor sets and use the averaged data to compute a position. My maths isn't too good though and I have yet to see what the drift factor is like.
The ODROID-W has a built in Li-Poly battery charger and is most similar to the Raspberry Pi Zero, although a little more advanced.
I'm pretty interested in this kind of work. The best of the luck in your try. If I can be helpful in any way, you know.