Here are some links and more acurate info.
http://www.xbox.com/en-GB/skyplayer/
You get 21 channels on your 360 free, wih no charge. All you need is your free Sky ID for existing Sky customers. Channels include all the Sky Sports and ESPN 1 and 2.
If you want to watch all Sky channels that you have on your subscription you need to have multiroom or Sky Broadband Unlimited. Or if you dont have these you can pay £5/month and access all the channels from your 360.
http://skyplayer.sky.com/aboutskyplayer/live-tv.html
And here is the link if you dont have Sky, and you want it for your 360. As you can see it is the same as normal Sky prices. £41/ month for example gives you ALL Sky channels available in there packs from your 360 Sky player.
http://skyplayer.sky.com/aboutskyplayer/online-tv-packages.html