Well see I'm planning to put electronics in the side, and for the eye some of the Borgs had a holo thing for the eye. I'm actualy thinking of re-doing the eye now that I look at it though.
When I built a Borg costume I used a kids spy toy headpeice that had the red laser that was mechanized (cheaply) and a halogram like mechanized peice that would move down the side of your head and then would drop in front of your eye.
I attached a flashing led to the eyepeice and some reflective tape and I had my Borg halogram! Cost was $25.00 for the spy toy and $5.00 for the led and tape.
Here is a close up pic of the spy toy modified with led's and automotive wire.