Jon- WAY too many variables to name a single $$$ cost. Low end- $1,000. High end- ummm.... how much money did you say you had?
Our place is double duty- storm shelter (had home demolished by tornado in 86) NBC shelter (downwind from a couple of nuclear reactors- ask folks in Japan about that) and wine cellar (nobody said you had to be miserable waiting out the tornado)
Yes, will probably never use it as an NBC shelter. Will probably never use that 20 lb ABC extinguisher in my shop either. But it is there just in case.
We equipped our place over the years, and on the cheap. Radiation meter? Paid $17 for mine, including shipping. Good surplus Civil Defense Victoreen 717 meter, runs on 1 D cell. Yes, been calibrated. You can spend a LOT more.
Filters? Series of filters, coarse to fine. Less than $40. Blower? Farm auction- blacksmith's forge blower- hand cranked. Potty? Camping store going out of business sale- but you CAN use a 5 gal bucket, trash bag liners, and a toilet seat. Lights? LED, Ni-cad, hand generator. Shielding? Filled core block, lined with books. Learned to lay block pretty good.