You don't need to extend Kirk for $20M AAV per season lol.
I think you can extend him for way less. Sean Murphy two years ago got 6 years/$73M at $12.17M AAV and was coming off a 5.2 WAR season and was 27-years-old.
As well, if I recall, there hasn't been a catcher in free agency who got big bucks over the last two years, so nothing really for Kirk's camp to compare with.