YES, I totally get sick of beans and rice. On the other hand, I grew up on it, so I'm sort of used to it as a comfort food -- and if I had to feed a lot of people very cheaply, that's where I'd look to do it. (Dal + rice and pickle/chutney, soups, chili, curry, etc.) If you're looking for variety, you've probably got to be willing to put more work/planning into the cooking.
I would plan your menus around the loss-leaders in the supermarkets, as well. Usually there are big sales on protein and veggies, especially during the summer, to get people into the stores. Stock up -- especially with anything that can be frozen or dried or stored for later use. Meat can be used more like a flavoring than as a main dish, especially if you want it to stretch.
Do you have community gardens near you? Or U-Pick farms? You could ask for the 'scratch and dents' or o pick through the abandoned plots in the community garden for vegetables -- especially tomatoes and zucchinis and watermelons/pumpkins.
Try shopping outside of normal US grocery stores. Scratch and dent stores and restaurant supply stores are great places to get oils, spices, etc. cheap. As are asian and indian grocery stores, especially for lentils and pulses, spices, noodles and sauces and sometimes yogurt. It's probably worth keeping a price book so you can stock up when prices get low.