$35 for the PI, $20 for a wireless USB stick, and around $50 for power supplies, wireless keyboard, USB hub, etc. and it's a very nice media player.
TheXPi.com sells three models of Raspberry Pi for different solutions:
The Bender runs XBMC for media center access to media resources on your network.
The Farnsworth is a video game emulator solution running MAME.
The Fry is a Raspbian Raspberry Pi solution with the straight Raspbian OS.
I have a Bender, and it’s amazing. Interfaces perfectly with my Synology NAS. Price is right as well.