Lava Tubes Could Reduce Cost of Lunar Base

Living in Lunar Lava Tubes by Ian O'Neill in Discovery Space

Ian: Personally, what would you expect the mission profile of a lunar mission would look like if we used natural shelter (such as lava tubes) to protect ourselves from radiation? Do you think this would be a cheaper alternative than building surface habitats?

Carolyn: Lava tubes would not only protect us from radiation, but also from meteoroid impacts and the extreme temperature changes over the lunar day. Near the equator, the lunar night is very cold (about -150 °C), and the lunar day, it is very hot (about 110 °C). A lava tube has a constant temperature, about -20 °C -- just like caves on the Earth have very even temperatures.
Not being an engineer, I'm not sure that I can comment on the costs of surface versus subsurface habs. It does seem to make sense that using a natural, easily accessible shelter would help reduce costs.