Get an inexpensive case. It's just a box. I know you are young and appearance may seem important, but getting the most bang for your buck on the components that really matter is the way to go.
Don't cheap-out on the PSU. The poor quality ones can take out your entire system if (when) they fail. See the Tom's Hardware PSU Tier list. You don't need the most expensive or most powerful PSU, but stay away from the Tier 4 or Tier 5 units.
Have you budgeted for an operating system, monitor, mouse, keyboard?