What is a cheapest way to feed 25000 tadpoles?

i need to find a cheap way to feed 25000 tadpoles!bullfrog tadpoles take 2-3 years to mature and i can let them go because the ponds are drying up and at lakes they have no chance. i cant keep feeding the frog tadpole bites it will gone in days and it is 7.56 per can. freeze dryed blood worms will be gone in a day 2.99 per small tube and fish is cheap but not that cheap.and algee will take months to grow,and and i cant sell them cuz the only people who want them a fishermen i tryed i need youre help