I dug this out by hand many years ago so I could have a secure storage at a retreat location. Its 12×15 in the main room. It has 5 foot of dirt covering the main room. I store food and survival goods here. Iam changing out the door and adding on to it. The cost was 0. The telephone poles where free,blocks for floor came from mobile home mover that just wanted them removed from a site. I covered the whole structure with 3 large commerical tarps that where free, the guy was moving from the country to the city and didnt need them. So just alot of labor.