well, depends what band you want to transmit in. a standard analogue TV channel takes about 6 MHz (excluding guard bands). if you want digitally, should take up significantly less. There probably are RF transmitter/receiver units for this on the market but in SA you'll have to look at 2.4 GHz since the 900 MHz was given to GSM (thanks icasa...). So the 2.4 GHz ISM band is your lowest option im afraid unless you want to get really low quality signal then you could maybe use 868 MHz. Just remember, 2.4 GHz is where everything is these days, from bluetooth to microwave ovens to WiFi. Personally, I would build my own transmitter receiver pair but try stay away from the 900 MHz ones (open band in the USA) since you could kill your phone reception or at worst have the fuzz at your door.
