How much did the St. Louis tornado cost?

That depends on which tornado you are referring to. St Louis has been hit by many tornadoes.

The St. Louis tornado of 1896 had a cost of about $20 million at the time, which is equivalent to a bout $570 million in modern amounts.

The St. Louis tornado of 1927 cost about $22 million at the time, equivalent to about $300 million today.

The St. Louis tornado of 2011 had a cost of about $30 million.