If there's one thing from this campaign that upsets the apple cart of arguments, it's that 'the only thing that wins elections is money.' Trump had fewer donations, had fewer big donations, had less money from special interest groups, and spent less money than Clinton, and he won. Although you don't hear this argument as much when your preferred candidate wins... When Obama outspent and easily beat Romney in '12 and McCain in '08, you don't hear this argument as much, but when Bush outspent Gore in 2000 or Kerry in 2004, it was a major campaign narrative.
This played out similarly in the GOP primary. He spent much less than the likes of Jeb Bush.