Here is something I believe in and have used ever since I started cycling, try before you buy. Any online ordering has the major flaw of not getting to try first. If you have whenching skills it might not be a problem but if not if you have a problem with the bike you are on your own. Do you have a bottom bracket tool to check the bottom bracket? Do you have a spoke wrench and know how to true wheels? If not looking at a used bike or finding one on sale is a better option. Do you have a Performance store anywhere near you? They have lots of commuter bikes and you can try before you buy. They have several fitness bikes in your price range.
http://www.performancebike.com/bikes...00316&metaData=
The problem I have is I don't know enough about what you need to make a reasonable reccomendation. Normally I say get a road bike with Shimano 105 or Apex minimum. For a 7 mile commute a Mountain Bike would work, with SRAM or Shimano shifters. I also agree look to a city auction and even garage sales.