Their black coffee isn't great, but their espresso is good which is what makes it into the sugary drinks. I think the main draw is that it's pretty consistently decent, while with other chains like Dunkin or Wawa you're never quite sure what you're going to get but it's probably not going to be that good. I'll also add that the coffee they sell at grocery stores isn't bad (although it's far from my favorite). I think it's much worse at Starbucks itself because it inevitably ends up burnt pretty shortly after it's brewed.

As far as price, it costs $2 because that's the price that Starbucks determined maximizes profit. From what I've seen at other coffee shops though including Mom and Pop ones, that price point is pretty typical.