We have a K cup machine at work which for the longest time I hated. I hated the idea of buying these expensive little cups that made horribly weak coffee. Then I saw you could get a refillable my K-cup but they run anywhere from 15-20$.
Well recently I found one on amazon for 4$ and picked it up. Let me tell you I was super excited to be able to use my own coffee (Bustello) in the K cup machine for pennies compared to buying their one timer cups. My excitement bubble was burst though on first sip when I realized it was even weaker. I was drinking hot pee water. Well with a little web search I found this indestructible (I LOVE instructibles) and it works and works great!