Cash sink. There is no way to hit high numbers without sinking cash. That being said, I have put thousands into this game over the years, only to still be broke. I also just lost access to my account as it was linked to a Facebook account that has since been deleted. Was told there was nothing they could do and I need to contact Facebook who also wouldn't do anything as the account is gone. Thousands lost. What a waste. Don't waste your time.