Every off season we hear about cost per WAR and how so-and-so player is worth his $15M because his two fWAR. This maybe true if you limit your sample to players with 6+ years of service time. But if you widen your sample to everyone the cost per WAR goes from around $12M to closer to $4M.
Now cost per WAR is not an end all be all. Teams don't use this cost per war as we may think, if they even use it at all. Bryce Harper is not worth $59M next season (if you believe Steamer's projections 4.9 fWAR * 12M $/WAR) Teams use other factors as well. Length of contract, Expected performance during that contract, Players position, Character, etc... there is a lot more too it. Teams also use other metrics such as cost per win and cost per run.
So what is the actual cost per war for 2018? It was about $4.17M across the league.
Is Bryce worth $20M next season? Mostly likely yes probably more, but it is a good baseline to start from.
Figured by adding up all the Pitching and Batting fWARs from fangraphs (1000.2 fWAR) and putting it against the total adjusted salary from sportstrac ($4.176B). You could go a couple steps father and do cost per pitching WAR and Position, since pitchers WAR and Position players are not quite equal.
The team with the highest cost per WAR was the Baltimore Orioles at $15.75M and the team with the lowest was the Tampa Bay Rays at $1.7M. The eight teams with the lowest cost per WAR all had records over .500, the four teams with the lowest cost per WAR had payrolls under $110M. (Rays, As, Brewers and Pirates). Eight teams where over $5m cost per WAR and two (Giants and Orioles) over $10M. Not one of those eight had a winning record.
After all is said and done, what does that mean? Not a lot going forward but its fun too look back on. Its useful for eye balling a players value if they're living up to their current deals.