Connorp has a point though, there is precedent for Realmuto. 31 year old Grandal signed for 4/73, 32 year old Martin signed for 5/82. Realmuto will be 30 years old to begin next season and is similarly valued to those two, arguably even less valuable - Grandal who is 2 years older projects to be better next season. He's a far better baserunner, worse defender and similar hitter. You can say his athleticism is better so maybe he'll age more gracefully, but he's still a catcher at the end of the day and he should be expected to age like one. Realmuto can aim for 5/125 all he wants but precedent states he should be very content with 5/100 if any team is offering that, and is likely to receive even less than that.
Another comparable - 30 year old Brian McCann signed for 5/85 with the Yankees.
I sure hope he's not aiming for Buster Posey or Joe Mauer money - both guys who were younger, franchise cornerstones on Hall of Fame career paths.