Transmitting AV signals one way
If you're talking analog, and you don't mind compromising quality somewhat, and you're happy to run cable, one solution is to use baluns to ship the signals over two pairs of a cat5 cable.  This approach has some advantages over an RF link in that you have your own private transmission path (the cable) so there are no licensing, channel sharing, or interference issues, but it is almost guaranteed to be lower quality.  I've seen it done over about 250m of cat5 in a building's cabling, and the video was definitely degrading.  Nominal maximum distance for colour video is 300m.  You can buy the baluns separately and assemble them yourself, or you can find pre-assembled units with RCA and RJ45 sockets in a small box, one box at each end.

Another alternative, somewhat more expensive, higher quality, but with the potential for interference is wireless analog transmission, typically in the 2.4GHz band but depending on local licensing rules they might be available at any frequency that someone will sell them to you.