Two of my friends got this and it's cheap:
http://www.trust.com/products/product.htm?artnr=12351
Works suprisingly well and there is 4 channels to choose from. There's Composite & stereo input/outputs and works with tv-out.
Another cool feature is that it passes remote-IR signals back to the main unit so you should be able to control your computer if you have the proper hardware.
Qualitywise, it's good. Walls is no problem, but people block the signal a bit and microwave owens could be a problem too..