If Panarin signs with Florida, he does not pay state income tax for the 41 home games.
So you could argue it's, at best 8.82% of half the base salary he would "save" in tax. 8.82% is the state income tax for NY. He would "save" $523,200. He however pays a much higher tax for every game in Canada. Florida plays 10 games in Canada this season. If he signs with the Rangers, it's only 7. Not really going into that much detail but it changes it a bit.
If the Rangers front-load the contract with 16.4m in the first 2 years and a 12m signing bonus, he gets 45m over the first 24 months. I am sure Florida can't match that much up front.
* I did not include the games in Tampa, Dallas, Nashville and Vegas since the Rangers play those as well.