Requirements:

☻ Cheat Engine
☻ Firefox or Chrome


Steps:
Go to FarmVille 2
Open Cheat Engine
Select -plugin_container.exe(firefox) or 2nd, 3rd or 4th chrome.exe(google chrome) or 2nd FlashPlayerPlugin_11
Value type to "Text" or "String"
Scan "coins"
Click the 1st address, Hold Shift and then click the last address
Click on the red arrow.
Select all the address (Ctrl+A), HIT ENTER
Change the value to "farm bucks"
Now, click on the farm expansion.
You can now expand your farm for free
You will get error after expanding. But on refresh, the farm remains EXPANDED!
HAVE FUN!!!