Hi B.,
I am the Mom of 2 girls: a 4 month old and a 3 1/2 year old. My 4 month old was placed on Similac's version of this formula due to an intolerance to milk-based formulas. She would develop a slight rash and spit up a bit. Due to this happening, they (doctors as well as our insurance company) consider it a medical response to intolerance, and therefore our insurance company pays for the hypoallergenic formula. I am not sure why your son was placed on it, but I am sure that it is probably a medical related reason. I would call your insurance company today to see if they will cover it. Unfortunately, doctor's don't tell you about this coverage- I am not sure why, as I learned about it from a friend. Most insurance companies cover this type of formula up to the child's age of 1...which is a financial lifesaver!
Now to answer your question, I have seen the large powder cans at Babies R'Us....but perhaps now you won't have to worry about spending the money for it.
Please let me know how it turns out for you...as I would be curious to know if your insurance company does pick up the bill for this....
Regards,
K. Q