Let me clarify. My post addressed the cost of each unit per unit of offensive or defensive strength. If you want max defense for your upkeep dollar, buy turrets. Max offense, buy jets.

Upkeep by NW:
Troops: $0.22/NW/turn
Jets: $0.23/NW/turn
Turrets: $0.30/NW/turn
Tanks: $0.285/NW/turn

All upkeep costs are + food consumption. At $44/bushel, the extra costs are
Troops, jets, and turrets: $0.044/unit/turn
Tanks: $0.132/unit/turn

Factor that into the above values and the total upkeep per NW per turn for each unit is:
Troops: $0.308
Jets: $0.303
Turrets: $0.3264
Tanks: $0.351