Actually, it comes down to understanding and justifying the mission/role and the need to prevail in that mission/role.
Arguments like the one you suggest got us aircraft like the Brewster Buffalo, the Devastator, and the Phantom with no cannon. Argument about mission/role -- winning the war, defeating the enemy got us aircraft like the P-51, the F4U (Corsair), the F-15E and the Tomcat.
Convince me the mission does not exist or is not worth winning, every time, and I'll buy the financial argument. It's not about exorbidance, it's about winning when you must.