Did you know Habitat for Humanity operates retail outlets where they sell used and surplus building materials? Habitat ReStores are located in 47 U.S. states and 9 Canadian provinces.
The person who writes about them on Cool Tools says,
I just refinished a garage for well under half of what I would have paid retail by buying most of the supplies from a ReStore—everything from the lighting to OSB board and 2×4′s we used to make the temp walls.
Find the nearest ReStore here. (Cabinets in photo were an actual ReStore purchase.)