[Walmart] Keurig Donut Shop Favourites Coffee - 40 pcs - $5 - YMMV
Nearby Walmarts show $5 here in Montreal, not sure if nationwide. You can check the stocks in your area:https://stocktrack.ca/?s=wm&upc=66344709740
If it's not in the coffee aisle, try to find it near the coffee machines. (Thanks @geogolem for pointing this out).