This cheat is really easy and actually works! You can use it more than once, whenever you like.
1. Make sure you're in your house on edit mode, then buy something expensive, or select the most expensive item you own. Don't worry, you'll get it back in the end.
2. Put it in storage.
3. Go to your storage and click the item, then select the option to put it in your room again BUT DON'T PUT IT IN YOUR ROOM.
4. Go back to your storage, select the item and sell it.
5. Go back to your room and tap an area on the floor. You should be able to place the item in your room, even though you just sold it!
Repeat these steps till you can buy something even more expensive, then repeat the steps over and over till you have enough money for whatever you want. Enjoy!