WOW, that's a wonderful price for flour! What brand do you use? The least expensive unbleached Bread Flour (milled at a local mill) is $2.97/5-pounds, or .44+ cents for 3 c. flour (5# flour = approx. 20 cups flour).
Other ways to bring the price down are to use a sourdough starter (which is made from flour/water) for naturally-leavened bread, or (as you already know) to purchase your yeast in bulk.
My #1 low-cost ingredient is to use freshly-milled flour, plus it's the only way to get all the 25 vitamins, minerals and proteins, as well as the benefit of the fiber from flour. Wheat is generally a fraction of the price of commercial bleached/unbleached flour and MUCH cheaper than commercial whole wheat.
Slight correction: 3 c. of flour doesn't usually equal a 2-pound loaf of bread - that's the amount normally used for 1.5# loaf of bread. Four cups will yield 2-pounds of dough. Scaling the dough will tell you the true amount. I teach bread classes and flour volume and dough weight is one of the things I always teach, as well as the proper pan size for dough amounts.
Even with the odd-ball ingredients I use, I make a recipe of multi-grain bread using 4-3/4 to 5 c. freshly milled wheat flour, 1/2 c. freshly-milled multi-grain cereal (coarsely chopped grain), kefir, chia gel, flaxmeal, coconut oil, agave nectar, 1 egg (or powdered whole egg), 2 t. SAF-Instant Yeast, 1/4 t. ascorbic acid, for around 50-cents for the recipe and it makes 2 regular loaves or 3 small loaves.
But anyway you add it up, we're both beating the prices at the store.