Where can I get the Brain Candy Mix on Neopets?

I'm doing a quest for the Brain Tree, and I have to feed the Esophagor some Brain Candy Mix to get the information I need for the Brain Tree. The only place I can find it is at people's shops, and it's waaay overpriced. The lowest price is about 33,333 NP. The highest is 99,999 NP. So where can I find cheap Brain Candy Mix?