Hi,
To date, there is no money cheat for the kindle fire hd as all the money cheats involves changing the date on your tablet which you can't on Fire HD. Maybe one day there will, but who knows..
But what I do to get money quicker is, I send them to work as usual and when they come back, I make them have a power nap (a deep sleep doesn't really matter as they are full green when they only get a power nap)and then, I make them do some gardening for 7-9h (while I'm at work) because they actually get way more money gardening than going to work.
It's not a cheat and you won't get millions in one click but it's still more money than only going to work.