For unit maintenence cost, go to the Economics Screen. Hover the cursor over it and it will show you the current cost per unit. This amount (cost per unit) goes up during the game. It is seldom a whole number which may explain the difference between deleting one unit or more than one.
I check this often in the game to compare the cost of a particular building with the cost of another unit. This can influence my decision at times when I already have a good army, things are calm (not at war or about to be at war) and my income per turn is low.
Missiles, by the way, do not cost any maintenance. Great People do.