A "audio video sender receiver" might be what your looking for they are cheap for 480i. They are normally 2.4ghz or 5.8ghz. If you want a high definition version check the professional video stores.
"audio video sender receiver" - Google Product Search < link, price low to high
I think I found what your looking for a HomePlug or PowerLine audio video that will run through the whole house. not cheap, They are sold as networking audio/video products.