How well thought out are the economics in Narutoverse (Konoha and other Ninja Villages)? Has Kishimoto ever explained it?
D-Rank missions were indeed overpaid, Kishimoto probably had no clue what he was doing when he said that 1 ryo equals 10 yen. But first, in each year, only 9 out of 27 graduates will be chosen to become a Genin, while the rest of course will be send back to the academy. This cuts down the quantity to the minimum, only 9 Genin are introduced to the mission per year.



Missions are assigned by either Jounin-sensei (if they still have a mentor) or Hokage himself. Almost all missions are non-repeatable, which means the completed missions will be removed from the mission list. However, it is the client who decides the amount of money to pay the village (you can refer to here), and then the village will pay the person who completed the mission. Not sure whether the village charges the fee or not, but probably yes in common sense.



Despite their high income, they might spend most of their money on ninja tools supplies such as shurikens, kunais, scrolls, bombs, etc. Shinobi use a lot of weapons and traveling goods, and that compensation probably is a supplement, rather than the real income.