In terms of every day living...
Linux. Cost: $0. Value - awesome. I can meet all of my computing needs with it, and I pay nothing.
Coal. I can start this on a gas stove and put it in my homemade heater and it lasts for hours. Next to buying wood, kindling, alcohol to start ect, coal is super cheap for winter heating.
Unrestricted/unlimited broadband. If a bit of an information junkie and save lots of stuff. Buying data blocks was expensive.
Going Vegan. Cost: Nothing but avoiding a few social norms. Savings in terms of groceries=enormous. People often think it's more expensive, requiring supplements. Nothing could be further from the truth. I buy no supplements and do not have issues meeting vitamin/mineral requirements.
I'm sure there's more, but that's off the top of my head.