I've been studying the metric Protein Per Dollar for the last 3 years. Some conclusions(feel free to google or check my profile for the link, didnt want to self promote)-

>Lentils and Beans are the highest Protein Per Dollar items, (~100g/$), Flour technically is among this as well

>Chicken Breast and Milk(likely because its government subsidized) are around 50g protein/$. Some pork(around 2$/lb is competitive)

>Eggs, ground beef, and tilapia are closer to 30g protein per dollar

After that, protein gets expensive.

>20g protein per dollar is pretty good for fast food, try the dollar menu.

Most protein powder is crazy overpriced. I found Myprotein Impact and Cytosport are 60-50g protein per dollar.

We eat for 20$/week per person, and we both lift heavy weights.

As mentioned, I have these studies on my website if anyone is interested http://efficiencyiseverything.com/food/