There is a lot to be said for a fallout shelter, and remember that a suitable structure will also give protection against fire, tornadoes, earthquakes and blast.

It could however be argued that a fallout shelter is less needed now than in the cold war era.
At that time there was considered to be a risk of large scale attack with numerous nuclear weapons. Shelter would then be vital, evacuation not being feasible if a large part of the country was affected.

Todays risk would appear to be terrorists aquiring a single nuclear device. Evacuation after use of such would be feasible as most of the rest of the country should be unaffected.

IMHO spending on just a fallout shelter might not be justified, unless it is designed to also withstand earthquakes, tornadoes, fire, and civil disorder.

An all purpose "doom shelter" is more worth considering.

I am aware of one in the UK.
It consists of an underground concrete shelter with 3 high security entrances. Food, water, and fuel are stored sufficient to shelter a family for several months.
It is designed to withstand the following
A direct hit with a conventional explosive bomb, such as a vehicle bomb parked adjacent.
A nuclear weapon detonation a few miles away.
Fallout
Extreme weather, including collapse of nearby buildings.
Attack with chemical or biolgical weapons.
Criminal or terrorist attack with automatic weapons, grenades, and demolition charges.