The plane I built last year uses a very low power Radio Shack video sender, and I was able to get the range you are talking about with it using high gain antennas. But it was heavy at 7+oz flying weight, needed a 12v power supply and the receiver antenna needed to be pointed at the plane. I have a video of it flying at my site.
http://www.rcsites.net/ia-flyer/
I bought the new 600mW Black Widow system here:
http://www.blackwidowav.com/productscore0524.html
And the camera here:
http://www.blackwidowav.com/CX161.html
I made my own cable to connect the TX, camera and battery using a connector like what is on the TX from an old VCR. Or you could use a deans connector.
I’ve just done bench tests and haven’t flown the thing yet, but with the TX in my house and driving around with the receiver, I was able to pick up a signal at 1 mile using the stock TX antenna and the 16dBi receiver antenna I plan on using. The signal was bouncing through and around several houses and obstructions because my house is in the center of town. Line of sight I should get 5+ miles and solid at 2-miles (fingers crossed).
I did a test using a 2 cell 650mA lithium ion pack regulated to 5 volts and it ran for an hour. Bill from black widow has 200mW systems that would be lighter and have less battery draw, and he has a 200mW ready to use package available. He also has wide-angle cameras if you plan on flying at lower altitudes or want a wider field of view.
If you don’t have one already you will need an amateur license to be legal, very easy to get.
Good luck,
Jim