Ahh, this has been on my mind for a while. We are on red clay and iron ore rock so it would definitely require expensive bulldozer work for us. There are some old storm cellars around here on properties that have less clay, more sand.
I have seen one-piece underground stuctures that are installed in a hole and then filled in around. I don't know what the real name of them is, but I think if you Google 'root cellar construction' you will find a lot of results.
Do you have a basement? If so build a small room in it as far away from the furnace as possible. Insulate it good and try to maintain a low temp. Mine is in a corner where the basement is in the soil half way up the wall, so that helps keep the pantry/root cellar cool. I maintain a pretty constant temp in the high 40s all year round.
Rural living can be challenging to the serious/curious/adventurous cook. Here's a place for the 'rurally challenged' to exchange info about our food wants and wishes, where we go to find what we want, and what we can substitute for that we can't find