Is getting this bike worth it?

I have no job (but looking) , I just graduated from High School, and I officially leave for Navy bootcamp November 22, 2011 (date might get pushed up earlier, and that could be anytime. I want to get in good cardio shape by running, and biking. I went to a bike shop, and saw a nice bike I wanted which is a Single Speed Trek Hybrid, I think it might be a Gritty I can't remember what the lady said the name was, but it looks like a Gritty. The bike will be around 430 after taxes, and that is a lot of money to spend on a bike to me. I have 500 dollars that I got from an uncle for my graduation present, I don't know If I would be spending it wisely on a 430 dollar bike, and on top of that I wanted a Go Pro (which I don't really have to buy) to record my bike rides. Would this be a good decision to make