Had a look most the amazon ones exceed the price of a second xbox or are out of stock, the ones that are cheaper are designed to beam your pc's dektop to tv wirelessly then connect by HDMI.
I think my googling sucks

I have seen a few AV transmitters, but the specifications are so vague, doesn't explain if it supports HDMI etc, such as:
weareelectricals.com/products/THOMSON-VS3010-Wireless-A%7B47%7DV-Transmitter-%252b-F3Y016CP3LG-HDMI-Cable-%252d-3-m
and
play.com/Electronics/Electronics/4-/14946839/SLx-5-8Ghz-Wireless-AV-Sender-System/Product.html?_%24ja=tsid:11518%7Ccat:14946839%7Cprd:14946839
and
mygamesandgadgets.co.uk/prod_show.asp?prodid=73178&ref=froogle
What's your views?