The snail idea sounds good.
I am surprised to see how few hobbyists culture their own Daphnia. It is so easy to culture in your backyard, even with very limited space.
All they need is algae and a bit of extra food. Before spawning time, I culture my own, but being on a farm now, I am considering to culture them in large quantities throughout the year.
All they need is a constant supply of algae which is almost free to develop. I add some cow manure and yeast on a regular basis.
You can harvest right through the year if you add light to your daphnia ponds during winter to keep the algae going. You place the harvested Daphnia in a freezer in ice buckets filled with 50% water and 50% Daphnia, and feed from there.
The nutritional content of Daphnia varies with age, and what its been eating. The protein content is usually around 50% of dry weight. Quite the opposite from Artemia, adults normally have a higher fat content than juveniles, about 20-27% for adults, and 4-6% for juveniles. Some species have been reported to have protein contents exceeding 70%.
Something to think about if you need to bump up your protein levels cheaply.