Which is the cheapest fpv sytem to use fot a dji phantom2 with h3-3d gimble and gopro?
(This includes the transmitter, monitor, reciver, etc)

There is no such thing as cheapest...you can always save even more, but I put a basic system together and explained it here:
http://www.droneflyers.com/2014/ ... quadcopter-project/

The most expensive part is the monitor on the ground - the problem is you usually get what you pay for! All in one units such as the one I used (battery, monitor and receiver built in) are about $140+.

Other than that, you only need a $25 transmitter and a composite video cord (or other cord, depending on GoPro model).

To really save money you can buy a 7" monitor (look on Amazon - these are used for car backup monitors, etc.) for about $30, then add a receiver ($30) and LiPo battery  for powering it ($20). In that way, you can probably put a system together for less than $100.
Note that your range and quality may vary - especially until you start tuning the system with better antenna's and the exact placement of antennas.