Cost-efficacy is, shall we say... politically important?

Explanation: Nader Shah was a reforming ruler of Iran, who replaced the old system of feudal tenure with a centralized soldiery that was professionally paid and trained, with the latest and most efficient weaponry of the time. With this, he won a great many battles, some with truly dire odds.

Unfortunately, between Nader Shah’s tendency to lay the taxation burden on the peasantry and his own… less-than-charismatic personality… he ended being quite unpopular in his own country, despite his successes, and was eventually killed during one of the many rebellions his taxation policies provoked.