Several years ago I was interested in these things until I discovered the cost of each flight and the very short duration. I remember reading somewhere that someone made one of these things in his garage using relatively cheap and available pieces. He also had a 100% safty record. $100,000 does seem a bit much.
The problem appears to be the weight to thrust ration. These thing just use a chemical reaction, ie not a motor as most people would understand it.
A motor large enough to produce enough thrust (or lift in this case) is currently too heavy to cary in the form of a jet pack.
But I agre with one of the other comments. It is nice to think about and would be cool to have.