By being lucky enough to always have girls in need of levels / evolutions. I have only reached over 1 million gold 2-3 times at most. At all other times I have had less than 500k due to constant lvling and evos. If you only lvl your best girls and not the rest then it's easy to save cash, but if you are a completion-est like me then all those 2, 3 and 4 * girls take a lot of lvling gold and a lot of manyu/dragon dailies.