Source: Aaron Gleeman, NBC Sports Hardball Talk 
John Mozeliak’s pre-signing comments about acquiring a shortstop were worth noting (via Derrick Goold of the St. Louis Post Dispatch):
One of the things we looked at when acquiring a shortstop was the amount of acquisition cost. For us, the asking price in the trade market seemed very prohibitive. There are two top shortstop candidates in the market, and one of the differences between them is there’s a righthanded hitter and a lefthanded hitter. We’re looking for a fit.