Cheapest would be earthworms, all you'd have to do is go outside and turn over some dirt.
I never cut them up, my toads like their worms fresh and lively, so they have something to wrestle with, it keeps them in shape.

Pill bugs/isopods/woodlice/rolypoly are also very cheap, go out into the woods and kick and old dead log.
woodlice are also a very easy culture to raise, they eat rotten vegetables, just get a container, dirt, maybe some crumpled cardboard for coverage, and keep one spot damp. They are also a rather meticulous and clean creature, not to mention the extra calcium is their shell will make them an ideal snack for your toads.

considering your climate, assuming you are still in your Fahrenheit's sixties an interesting trick would be to lay down a wet loose newspaper in a shaded spot. return the following day and see what kind of selection of creatures you see fit to sentence to death.