I did this calculation a while ago (didn't include hot dogs, because 🤮). But whey protein absolutely stomped every other protein source in terms of cost effectiveness. This really isn't surprising considering it is a dehydrated, shelf stable source of pretty much pure protein, which also (iirc) is a waste product of cheese making. So you are basically buying something they want to give away for free, which has no cost to keep it cool, no need to move product before it spoils, no additional weight of water or bone to transport. They just add some flavoring and sweetener and bam! You're jacked!