Thanks - Mahomes' new contract would start in 2022, not Allen.
Also, if the Bills pick up Josh's 5th year option, it sounds like his salary will be pretty high (and the cap hit) based on this ...
The option for top-ten picks is set at an amount equal to the salary of the Transition Tender (set in Article 10, Section 4 of the CBA) for the player’s fourth contract year. This salary is calculated, to put it simply, by finding the average of the top ten highest Prior Year Salaries for players at the same position. Positions are defined by where a player spent the most plays during the previous season (Sec. 7, (a), 31), unless you ask Jimmy Graham.