My local Eckhard wanted like $8 for a pint when I was using PG. I want to suggest you get premeir media beads instead, they are really THAT much better.
If you still want to go the PG route, you should look to an animal feed and supply store or perhaps a vet. PG is used to treat and prevent ketosis in dairy cows and also to dilute other meds. You can get it for around $12 a gallon from online animal health product stores, so I suspect it won't be much more at that sort of place locally. I find its much easier saying "I recon Bessie's got the ketosis again" than explaining why you need to maintain a specific high humidity level in a small closed envronment (can you say shrooooom?)
Matt