This is a simple achievement that will just take a bit of time. I would generally just check the game once or twice a day after work or leave it run next to me while doing something else. I as able to get this in about a week and a half of slow progression.
If you just want to focus on reaching this quickly and are actively playing is keep resetting your free play runs and putting all your money into click damage until you can't progress, then repeat. This will help you increase your favor, thus increasing your gold find which you will need to reach the higher amounts of gold.