Safe rooms can be retrofitted, but that can be very expensive, having to tear out walls and such. FEMA suggests, for a lower-priced option, to build an entirely new structure within the house, preferably in the basement or garage. It's not really the kind of project you want to do yourself; they have to be anchored in the ground, and the materials are necessarily difficult to manipulate. FEMA estimates that a family-sized safe room, which could double as storage or a closet, should cost around $6,600 to $8,700. There are theoretically programs to assist homeowners with this cost, although they won't cover the entire project.