The $30K GT500 in your link is listed as a $75,000 buy it now, and the bid is sitting at $55,000 as of right now.
As a Mustang owner, the GT500 is way over your head for a first car. You need to crawl before you walk. Take it from an old guy. If you are getting a car and like the Mustang go for a 2012 or 2013 3.7L V6. Go drive one. They are good starter cars to learn. Spend time with it through college. When you get a long term full time job afterwards, then look at buying a 'fun' performance car.