One of the confusing things that happens when a person asks a question in these forums if you hardly ever get a simple yes or no answer. People have different needs and different budgets and it is always easy to find a better wheel but at a higher price. Just look at the questions when someone has posted they have narrowed a decision down to two bikes, a specialized something or a Trek something else. Three posts after asking the question someone will suggest a Giant or Kona and a post after that someone will suggest they exceed their budget. They are simply trying to be helpful and are speaking from experience but it doesn’t answer the question originally asked.
I don’t dispute any of the post so far. There are some positive points that relate more directly to your question. The positive thing about the Aksiums is they are lighter and stronger than your stocks wheels. They are a good deal from Nashbar because they are about 40 percent off and under your budget. MY LBS couldn’t get a better deal. They also have cartridge bearings and tend to stay true longer than stock wheels. So simply the answer is yes, they are better than your stock wheels, yes you will notices the difference in ride, and yes they are a good deal. No they will not be the last wheel upgrade you ever look at and no they are not the best wheels out there. Just get a picture of a set of ZIP wheels and put it on your closet door.
Are there other good wheels out there and other options, sure but will they fit your budget and are they on sale?