Honestly, I don't really buy into the idea that getting your protein from a mix of beans and grains will somehow cause you to end up making up the cost difference in medical bills due to the amount of carbohydrates you're ingesting, given the huge number of people on this earth who do so and who appear to have perfectly fine results from this sort of diet. Just make sure you're getting some exercise (which you should be doing regardless of your diet).
That all having been said, tofu can be quite cost effective, low in carbs, and high in protein. Of course, you might tell me there's aggression issues associated with tofu ingestion, and that it contains chemicals that mimic estrogen. So, there's seitan, which is also high in protein, low in carbs, and can be made relatively cheaply from wheat gluten in bulk. Of course, there are lots of people who decry wheat gluten as well, not to mention people who're legitimately allergic to it.
So that brings us to meat and fish. Meat often comes along with saturated fats and often raises your blood's LDL cholesterol levels, not to mention all the health, environmental, and ethical concerns of factory farming. You could take part in a co-op for your meat, but that is not going to enable you to eat for especially cheap. Fish is generally better in the fat and cholesterol departments, but many carry with them mercury content that makes a lot of people nervous and the threat of overfishing. There are fish that avoid most of these concerns, such as tilapia, which fit most of the criteria, but is still not anywhere close to as price effective as dried beans.
If you don't want to get your protein from beans, that's fine. I personally advocate people pay a little more and eat a healthy, varied diet, including many (or all) of the above-mentioned dangerous foods. But this crap about "medical bills are expensive too" implying that somehow eating an incredibly traditional and largely vegetarian diet will send you to the hospital is just ridiculous.