Coffee Bean Direct -- from which I occasionally order coffee for my tasting events -- includes this K-Cup infographic in its pitch for a reusable filter for Keurig machines. This graphic provides details that I did not include in my earlier screed on the topic, entitled Will Convenience Kill Coffee? I especially appreciate the research on waste streams.
Several other methods are less expensive and more effective while requiring about the same amount of effort. A small French press can make single cups that actually taste good!