One, K cups on their own can be expensive per ... And this is it: only fill the reusable cup filter basket as high as the stainless steel mesh is. Any higher and the water may overflow the top ...

Then I found the My K-Cup Universal Reusable Ground Coffee Filter. It's an inexpensive reusable coffee filter that fits any Keurig-brand at-home coffee machine, so you can use it however many ...

You'll save the most, and limit trash, with a Keurig K-cup adapter. Annual cost after initial purchase: $80. Use your own coffee; reusable cup and reusable filter.