Randal Grichuk
Value-wise, Randal Grichuk may be the best "bang for your buck" option the Cardinals could pursue to upgrade their lineup against left-handed pitching.
Grichuk is having the best year of his career since he broke out with St. Louis back in 2015. Playing in Arizona, Grichuk has posted a .287/.343/.434 slash line with 2 HR and 18 RBI in 143 plate appearances. With that sample size being so small to this point, I do think the Cardinals could swoop in and grab him at a bargain price while reaping the benefits that Grichuk provides.
In 95 plate appearances against left-handed pitching, Grichuck has posted a .310/.368/.452 slash line (132 wRC+), exactly the kind of boost the Cardinals could use in their lineup. The Diamondbacks have mostly platooned Grichuk this year, but he has been just a hair below league average against righties, an encouraging sign if St. Louis needed him to play more.
Like De La Cruz, Grichuk has not played any center field this year but has in the past. Grichuk would not be a good defensive center fielder, but he could hold his own if asked to do so, and the Diamondbacks have plenty of center field options on their roster that limit the need for Grichuk to do so.
I like Grichuk as a fit over De La Cruz due to the familiarity St. Louis has with him, as well as the lack of team control. No need to pay extra for control for a guy who you really just need to fill a role down the stretch this year. Watch out for Grichuk's name as the deadline draws near.