A cheaper alternative to the Harris cassette is Shimano sells an 11-30 9 speed cassette:
For $18, it is a pretty good deal. But two things about them. First, there's that 11t small cog that many don't like. Second, I found the quality of Shimano HG50 to be mediocre. It just doesn't shift as crisp as my ultegra/dura ace cassettes. Still, for $18, it is definitely worth a try. Good Luck!