I got some lovely organic castings from www.monroeworks.com and they had a 40 lb. bag for $32.95. Shipping on top, of course.

Here is a link that might be useful: Worm Castings under $1 per pound

It is pretty easy to make earthworm castings in your own home by raising red wigglers. There is lots of good info at the vermicomposting forum. Of course, you will need to buy or find some red wigglers first and wait while they turn your kitchen garbage into to "Black Gold".

I've found a source in Socal that sells it for $1/lb, but I'm sure there has to be a better source. They sell it by the yard so it's definitely a large production.. unless $1/lb is relatively good?

Vermicomposting is a possibility in the future but not at the moment. :(

OMRI listed castings cost a little more. That site for Monroe Works is moved.

Here is a link that might be useful: Worm castings under $1 pound