I'm not a coffee drinker, just a tea drinker. The Keurig is an expensive machine just for heating up hot water to toss in my own tea bag, but at 50 cents a cup for the k-cups, it's expensive that way too.
They do have the "My K-Cup" too, it's a mini filter designed for the brewer, and you add your own coffee to it.
And if you do buy in bulk, there is the k-cup swap on the board.