Maybe at a more expensive convenience store, or he's like many idiots that shop somewhere like Whole Foods and because they're used to seeing some $70/bag organic free-range non-GMO gluten-free coffee grown in the Himalayas by a small sect of previously uncontacted monks, the "cheap stuff" is the $20 bag of stuff that's similarly overpriced.
The most I've ever paid for coffee in the US was $20/lb at a local artisan roaster, where they're blended and roasted right in the store. Usually my normal coffee is about $3-5/lb
Then sadly, knowing how a lot of my friends shopped when they were broke, I bet that it is something like a convenience store. Not saying that DC isn't expensive, I was literally just there visiting a friend who lives there, but I also live in an area with a CoL well above the national average and coffee still isn't $20 for cheap pre-ground stuff