Breeding silkworms? I find that to be too expensive... especially if you can't afford importing mulberry. I bred African Land Snails, Brown Field Slugs, various species of cockroaches, European Nightcrawlers, Red Wigglers. My friends give me minnows, locusts and crickets in exchange for some of my stuff.

MICE! RATS! GERBILS! RABBITS! FINCHES! CHICKENS! QUAILS! MINNOWS! CICHLIDS! LIVEBEARERS! SNAILS! SLUGS! BEETLES! MOTHS! COCKROACHES! LOCUSTS! EARTHWORMS!