It's not as convenient, but a moka pot makes the best single serving coffee I've experienced. You can get a small version for less than $30. It takes me less than 5 minutes to make a barista level cup, and even the more expensive coffee is going to cost less than 50 cents per serving.
The only downside is the coffee is highly caffeinated--nearly espresso levels. So you're forced to add water if you just want a "cup" of coffee and it's more of an Americano-style. But the taste beats the shit out of drip or Keurig cups...imo.