I've got the perfect suggestion, and it's totally not gross at all.
Greg Sewitz, the co-founder of Exo, a startup that is working on a line of cricket protein products (starting with protein bars), discussed how cricket is a complete protein source with 2.2x more iron than spinach. And! For every 100 pounds of feed, crickets yield 60 pounds of edible protein, vs. 30 for chicken and 5 for beef.
Sounds like cricket protein is a solid alternative.
And, as it turns out, the bars don't actually taste like crickets. Nor do they feature any pictures of crickets on the wrappers or containers of their products. The reason is because, although 80% of the world eats insects on a daily basis, Westerners still feel a bit of a ick factor when it comes to eating bugs.
If nothing else, I think Exo bars are worth trying. As far as cost -- they'll run around $2-3 each. Which is pricier than a Cliff bar, but cheaper than about 90% of what you'll find at Whole Foods.
Want to know more about crickets, protein and sustainability? Check out this infographic.