Value is a tough concept to quantify. There are plenty of statistics in baseball that can help one find what a player contributed on the field, but to me, value can best be described as getting the most of something for the lowest cost. When grocery shopping, I find the most value in shopping at stores like Sam's and Costco because I can get the most amount of a product for the best price.
In baseball, one of the most all-encompassing statistics when evaluating players is Wins Above Replacement (WAR). Both Baseball-Reference and Fangraphs produce their own WAR statistics, and both can be useful for player evaluation. It is a simple equation to find out which player provided the most value using WAR and that player's salary.
Dividing a player's salary by his WAR total can give you how much one Win Above Replacement cost that team that year for a particular player. Whichever number is closest to zero indicates the player with the most value. The greater the number above zero, the worse value that player provides. If a player has a negative total, then they lose the team money based on their performance.
I decided to put this into practice to evaluate which players on the 2023 Cardinals' roster were indeed the most valuable. Typically, the younger the player, the less they cost a team due to arbitration and pre-arbitration salaries; older players may garner more WAR, but their salaries make their value much lower. Therefore, we will find that young players were the most valuable, which explains why teams are eager to trade for young, controllable players.
All salaries are pulled from Spotrac and all WAR statistics are from Fangraphs. If you would like to explore my math and charts more closely, here is a link to the spreadsheet that I created. In order to make it the most accurate, I used players who had exceeded 100 plate appearances as a position player or thirty innings as a pitcher.