Mac and Cheese Powder: Math not adding up?

I'm wanting to try bulk cheese powder and noodles instead of the blue boxes. However...As I do the math, it's not adding up? I'm treating a box as a single serving, with my eating habits.

2.5 pound tub of cheese powder: $30

Estimated ounces of powder in a Kraft packet for a standard serving: 2

Servings per bulk container: 20
Cost per serving of cheese BEFORE BUYING NOODLES: $1.50

Cost of a single box including noodles at Walmart: 0.58 generic, 1.24 name brand.

Am I miscalculating how much cheese powder I need, or is it cheaper to get Walmart boxes than the bulk cheese tub off Amazon?