Ryan Helsley
Oddly enough, the most valuable (and realistic) trade chip the Cardinals may be able to leverage at this year's trade deadline may not be a starting pitcher or big time veteran bat, but rather, their elite closer in Ryan Helsley.
Helsley's value is multi-faceted. First, closers like Helsley do not grow on trees and are often times one of the most sought after players on the trade market for their ability to be a literal game changer. Helsley has a 1.50 ERA in 18 games so far this season and has been lights out at the end of games for the Cardinals. Having a guy who can throw 103 MPH out of the bullpen with nasty breaking stuff as well is a huge advantage come October, and teams who think they can run the table in 2024 will want to get in on that.
Second, Helsley is under team control for the 2025 season as well, so any club acquiring him is adding them to their bullpen next season as well. Two playoff runs with a closer like Helsley is worth a lot on the market, and past trade deadlines have shown us that.
Josh Hader was dealt to the Padres with similar club control remaining but was having a really bad year with the Brewers so his value was lower than it could have been. The most famous instance of a big-time closer being traded at the deadline was in 2016 when the Yankees decided to do their own little retool, trading Aroldis Chapman to the Chicago Cubs for the 24th-ranked prospect in all of baseball at the time in Gleyber Torres, as well as pitcher Adam Warren and prospects Billy McKinney and Rashad Crawford.
Chapman had just half a season left on his contract, but the Cubs paid a haul to grab him so they could go on and win the World Series. While they may have overpaid a bit to break their curse, I think a similar package would be very possible for Helsley given the extra year of club control he has.