Protein Powders supply the most grams protein per buck spent.
Tuna, which is the cheapest food product that has a lot of protein, has shot up in price in the states as of recent. It's about .79/can which comes out to 46.84 g/dollar. Standard 5lb tub of protein powder can be bought for 30 bucks (including s&h) and it usually has 110 or so servings of 20g of protein. That comes out to 73.33 g/dollar.
This time last year, standard can of tuna was about .59/can. This gave you 62.71 g/dollar. The can would have to be 50 cents to beat that price.
It's too bad we can't go to the grocery store and set forward prices for us (the consumer) to pay months in advance. Better yet, with the rising tuna prices, you could buy a call option on them and make money on the price hike.
Oh wait, looks like I got on a finance rant! Hopefully, my point was well taken!