I will only use USP labeled products for vaping. For a local easy source the Humco brand glycerin is USp and found at many Walmarts, in mine for 3.88 for 177ml.
On a side note I refuse to shop at CVS any longer. While I no longer smoke thanks to vaping, any company refusing to carry tobacco products in an effort to force the decision on us is no longer worthy of receiving my money. And if you think they will stop at just tobacco products think again, let get away with it once and they will keep making choices for you. Speak with your money and tell them that whether they agree with it the choice should be yours not theirs. Otherwise the next product line they won't carry will be anything used for vaping.