A little late on the reply here, but you might want to look into "Textured Vegetable Protein" (TVP) from BulkFoods.com, it is 53% protein, goes for ~$2/lb (shipped free), and it mixes in with regular ground beef without giving you some kind of funny flavor.
link. Extra lean ground beef is only about 20% protein by weight, so TVP is a pretty good deal, like $0.86/lb extra lean ground beef, plus there's less volume, so it's easier to eat more. Also, it doesn't go bad like fresh or frozen ground beef.