Cost to hire staff from other teams

As Toronto FC I was trying to approach Chris Armas for a coaching position but he refused to talk to me (which in and of itself seems unrealistic, though he is/was at New York) so I put him on my shortlist and forgot about it. A while later I got a message saying Seattle had offered him a contract and that New York would be due $65k if he accepts. Hoping I would be able to get him instead, I go to offer him a contract the same day I got the message. We've come to terms but I'm still waiting to see which team he picks. However I will have to pay $96K to NYRB for him to join. Why the difference between those two amounts? What are the factors that determine this?