Newly released, think this may be the cheapest. Works on all the realteks, ACRyan, Xtreamer, Mede8er, Cyclone, Ellion, etc.
Scan (this weekend only) - £16.43 (cheaper if you get free postage on a big order)
Ebuyer - £16.56 item number 195483
The Sumvision 300Mbps Wireless N USB Adapter allows you to connect your Cyclone MKV to a wireless network.
Designed specifically for Sumvision's Cyclone MKV series, the Wireless N USB Network Adapter allows up to 300Mbps data transfer rates, ideal for streaming multimedia content over your wireless network.