I have a stockpile of still-in-the-package polyester/spandex tights that I found at a GoodWill after they didn't sell at a sporting-goods store. They were for women, so I don't get the easy access panel for road side relief, but otherwise fit the same as a men's thermal tight.

I have a stockpile of merino wool garments for layering, bought new from stores like Ross, Marshall's, etc. when I find them for an excellent price. Picked up a few Columbia fleece tops this way too.

If you are watchful, year round, you can build a good collection on the cheap.