Variants are different between FA cost vs NON-FA
There are factors that make the cost vary in free agency:
1 - The Quality of the free agency.
2- The free agent market is volatile and sometimes lacks common sense
3 - The need for a team with a stupid manager (Moore-Vargas).
4 - The team economic power (Phillies, Dodgers)
5 - The performance of X player year before free agency (Johnson down, Ervin Santana up)
6 - Draft picks
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How much the Blue Jays need to invest to reach 90 wins?