You can dig a tunnel that is at least 6ft down and 100ft long that leads into your home at one end and up to a narrow opening on the surface on the otherside. Then add a fan that blows air from the tunnel into the home. This will function as a natural AC unit. It is a lot of work to accomplish but can cheaply cool a home as long as its maintained. The science behind it is that the temperature under the earth past 6ft is around 55 - 65 degrees Fahrenheit depending on your region of the world. The fan will then draw the air through the tunnel where its cooled and pushed into the home. The tunnel doesn’t have to be that big just like 2ft in diameter. Though mold can grow here so you would want to use a material that is resistant like a smooth walled plastic pipe for your tunnel.