A couple of things.
1. Good choice on the Antec case. There is no better case in this price range. Very good cases, yes. Better, not IMO.
2. There are many places to get Antec cases.
3. "They install the power supply for you". The Antec and most other cases come with the PS already installed. If you ordered a different one, it's only held in by four screws and would take exactly 30 seconds for you to figure out how it goes in and to do it. Good luck.