Texas Tech's Wind Science and Engineering Research Center is probably a good place to look for information.

The usual problem guys run into with building a monolithic dome is the need to drive over to the wife's house to visit the family...

I don't see why an in-house shelter would cost $50k unless a lot of remodeling is done. The tricky part might be anchoring the shelter down in case a tornado throws a tree through the front door.

For the curious the website for David South's Monolithic Dome company is here.