I buy on e-bay. My son is on Neocate. I know most of it is probably left overs from someone else, but it is always sealed, and usually sealed in the original box. I was buying in store, but we get no help from our insurance and in store in our area is $37 per can. I just bought on e-bay yesterday 7 cans for $17/ can.
It’s all in what you feel comfortable doing.
Otherwise, I have no advice. I know that almost anywhere you buy online, it’s going to be about the same in store after the shipping. From what I have found…… Others may have better advice.