Safecastle's experienced shelter builders (20 years and 500 shelters around the USA) provide some of the most robust, yet cost-effective shelters available. Storm shelters, safe rooms, NBC fallout shelters, and now also military-grade bomb/fallout shelters are made of heavy-gauge steel plate ... engineered to last almost 100 years, lifetime guaranteed for structural integrity.
Shelters ranging in value from $5K to well over $1M have been built and installed for private households, corporations, communities, and government agencies.
Have a look at some 3D modeling of a 50-foot Military-grade Fallout / Bomb Shelter.
See also the Safecastle shelter site with much more info, images, price lists, and video--including clips of The Weather Channel doing their best to destroy one of those shelters - very amusing, entertaining, and impressive.