I highly recommend you watch the video series How to be successful in FPV by Ibcraze.
A 200mw 5.8gh video system can easily go 1/2 mile. I have gone about 2 miles. Many factors effect the range.
Antennas are everything. Not the cost of the antenna but the placement and style of the antenna are very important. I recommend recording your video on the ground. At some point you will have a failure and lose your plane, the video will be invaluable to find your plane.