Root Cellar - the author said it cost about $1,000 for this 8x8 foot cellar: concrete blocks were $1 each at the time, and he used about 320. About $500 for concrete and mortar, and the remainder for rebar, wood, etc. He contacted a local gravedigger to use a backhoe to dig out the space for the cellar.
How To Build A Root Cellar – Tutorial
Poured concrete arched roof. Complete buildout with commentary
How To Build A Root Cellar
Guy ripped his garden up and built an underground mancave.