"I'm not selling bongs at a booth in the Flea Market for the love of God!"

Hahaha!! too funny!!
I agree with Playfelt, you are positively doing fine if you are asking the going rate and alot of parents are looking for the organic benefit that you are providing.
Besides giving it more time, maybe try to advertise in different areas. Besides on this site, try kijiji, posting ads at schools, playgroups, on mailboxes in your area, even stores if they allow it. Here in Kingston, I would advertise at a shop called "Go Green Baby", where they sell cloth diapers, naturally made toys, organics etc. Also at Universities and Colleges could provide you with a different market.
But whatever you do don't budge on the rates. You are right, we are not bartering our salary, and you deserve the extra due to the expense in food!!