How do you know its the starter? Can the starter be twisted and removed? Fluorescent lights dont always have serviceable starters. The ballast may be bad but you would have probably been warned by longer and longer turn on times. The bulb could be bad without warning.
I would buy a cheap lite from the hardware store and take the fixture to an electrician or lamp shop, even the lighting dept at say HomeDepot or Lowes might help you out.