If you live near a tractor supply store, they may have PG USP for about $20 for a full gallon. It's used for treating a skin condition. As long as it says propylene glycol USP, nothing else listed, it should be fine.
If you are okay with vegetable glycerin, Glycerin USP is available in most pharmacies, typically near the bandaids and isopropyl (rubbing) alcohol. It is labeled Glycerin USP, typically called Skin Protectant, and the ingredients will only state Glycerin 99.5% (or higher), possibly with the word "(anhydrous)". Costs $4 - $6 for a 6 ounce plastic bottle. It is clear, thick, fine to use if your 36 mg nic is a PG base. You'll get more vapor, though a decrease in
throat hit, compared to using PG.