Amateur TV is limited to those who hold a Technician Class or higher amateur radio license. If you don't have a license yet, I highly recommend getting one. ATV comes in several different frequencies; 70cm(420-450 MHz), 33cm (902-928 MHz), 23cm (1240-1300 MHz), and 13cm (2390-2450 MHz). This gives you a wide range of frequencies to choose from to avoid RF interference.
I used the 434 ATV transmitter from www.hamtv.com, which runs about 99$. This can be received on any TV that can receive analog cable signals via channel 59. My receiving system consisted of a 5-element Yagi antenna tuned to 434Mhz connected to an old VCR outputting to a small LCD monitor (the older VCR had better reception than a newer hybrid TV). I tried to use a USB TV Tuner at first, but I could not get a signal unless the transmitter was very close (they have very weak pre-amplifiers) and there was a buffering delay of about 2-3 seconds. Not good for FPV.
My range for the 100mW system ended up to be approximately 2500 feet. Next time I will get the 5 Watt version for another $100 that will give me much more range and will allow me to drop the VCR from the setup and just use a cheap portable LCD TV. Maybe if I am really ambitious, I will even pump the power to 20 watts with an amp.
Overall I was pleased with the system I had slapped together on a tight budget. The transmitter module was easy to use and, thanks to the circuitry being potted, even survived a 70 mph crash into the desert floor.