Black beans: I buy them in bulk at either the local mexican grocer or walmart (before we moved), and now I do costco or a restaurant supply store. Although lately we haven't done many beans, so we buy the 1lb bags now, but they're HUGELY more expensive. You don't want super old beans though- be sure to store with NO AIR (ie, press all the air out of a ziplock or similar) otherwise they won't soften as well when they cook.
Since getting my instant pot, I use that. Before, I would soak overnight and then boil on the stove. The soaking reduces cook time.
Rice we still buy at costco. 25lb bag of jasmine rice works out to like $0.52/lb.
We cook rice on the stove. Bring 2cups water to a boil, add 1 cup rice, let it come back up to a full boil (covered) and then reduce to a simmer for 20min cook time.
This is the no seasonings approach- I highly recommend adding flavor at every step possible. Chili powder and onion powder with the black beans as they cook, chicken brother in with the rice or salsa added after, stuff like that. And we put red salsa and salsa verde on *everything*. Easy way to get veggies in there, and flavor. Be sure to add salt to your meal before you serve it, and some fat (like butter or sour cream), because that's what punches up the flavor and helps you feel full from it.