I have family & friends near there and generally there is no discount as it does not actually protect the home (what is insured) only the occupants, but some life insurance companies offer a credit for them. The most inexpensive option we used on the farm (aside from a simple earth shelter) were LPG tanks. Simply cut one in half, weld a plate to the opening, cut a hatch and hinge it, then anchor to the slab. You can make two, two adult shelters for under $1k and it only takes up about 10 sq/ft of a garage floorspace. Typical tanks are 3/8-1/2” and more than capable of withstanding an EF-5 (3/16" flat plate has been tested/rated to 250mph in above ground applications).