In Kentucky, underground storm shelters typically start around $5,000 installed, with prices increasing based on the number of occupants the shelter is designed to hold. It's unlikely you could build one yourself for that cost, so I highly recommend considering a pre-fabricated, professionally engineered option offered by many companies today. Some even offer models that can be installed beneath your garage floor, allowing you to access the shelter without having to go outside during severe weather.
Regarding the door,
many residents in the area notify local authorities after installation so they can be added to a registry. This ensures that, in the event of a tornado, rescue teams know to check for you and can assist if the door becomes obstructed. In my opinion, the door isn't a major concern, as these companies have already thoroughly planned for such scenarios.