Recently I ordered for my Cheerson CX-20 drone an FPV kit from Bangood for 157 USD:
Cheerson CX-20 RC Quadcopter Spare Parts 5.8G FPV Image Transmission Device Set
For a video, scroll to the end.
The monitor (model Sky-702) alone is worth 140 USD and it has the (removable - in case you don't wanna use them) parts to protect it from the light (you know, when you are on the field to avoid the sunlight in the screen).
The kit provides also the necessary part to mount the monitor to the transmitter. Included is also a clover antenna (worth 20 USD) and some cables for it. See some close up photos of the transmitter and the cables for it.
On a first look the cable seems to be a micro USB but it's not (I tried to plug it in my phone without success)
I tried to plug the cable in my GoPro 4 HDMI plug, but the cable is too big.
The manuals provided with the kit are kinda useless. They just show some details about the channels, but no information to understand the wiring or some other more important technical details. Also the support from Banggood is quite useless. I wrote in the forum asking for info and no useful information was provided, besides telling me to e-mail the customer support and ask for the manual. So I did and I'm still waiting for it. As the documentation and manuals are useless, I'm updating this article when I'm doing progress... see updates.
The transmitter looks like the SKY 8200, so when I'll ask for help in the forums I'll point to it. For more close-up pictures and technical details about the SKY 8200, check:
The following is my try and guess testing (and so far it didn't work). TO BE UPDATED. HELP needed.
The main challenge for me was to make this work with my GoPro 4 Silver edition. The kit doesn't come with the cables for the GoPro 4 and also the customer support on Banggood had no idea on which cables to recommend. This is really bad from banggood and even from Cheerson. I have no idea if connecting the transmitter to my drone like I did is correct or not.
I bought a USB cable for GoPro 3 for 3 USD and I tried to connect it like this (see following picture)
The 2 G+5V (S1 and S2, bottom left) are used already by my gimbal (I didn't put it to simplify the picture). The clover antenna needs 12V so you must get the power from the drone, from one of the G+12V on the right.
I had to go to a local hobby shop with the GoPro cable I bought on banggood and with the cables provided by the kit and ask to combine them together. The result can be seen in this video. It works!
Update February 2016: if you don't have a local hobby store in your nearby have a look at this FPV 5.8GHz 200mW Mini AV Transmitter For Gopro Hero3 for 28 USD (it includes both transmitter and cable). I've read it works also for the GoPro 4. You may need to cut the red cable. See "Questions & comments" in the page for more details.