Couple of points on this:
1) Jail breaking is free, the apps are free as are any of the plugins, anyone that tries to sell you it on any other basis is a muppet.
2) Jailbreaking is easy if you can get a device.
3) The problem comes as supply and demand, right now the ATV2 is the only box that can be jailbroken but is no longer purchasable from Apple. ATV3 has yet to be done.
4) Ignore anyone that tells you that you are getting channels etc. natively. You can't do this unless you have the equipment/plugins to support it. (See point 5)
5) ATV2 is a media streamer. Period. Therefore it requires a source, such as cloud based storage or a local server, NAS or PC which hosts the content. Some plugin's like Navi-X will allow certain worldwide channels (don't expect a SKY UK package or them all to work). SportsDevil will stream worldwide services (baseball etc). Additionally you can stream content from a local enigma2 receiver.
6) You can buy ATV3 for less than £90, however the cost to rent movies or tv shows from apple is expensive, you can of course use it for Netflix or Lovefilm, but both require a subscription. To me it's nothing more than a door stop in this form (non jailbroken)
Navi-X 3.7.6 on XBMC
Navi-X is a "content aggregator" app that provides access to all kinds of multimedia content, listed on a public directory of user contributed listings or playlists for playing on your TV, PC or mobile devices! Users can link to content and playback video, audio, pictures, podcasts, text, rss and html on the internet and share it with people around the world in seconds! Create fully customizable playlists with backgrounds, logos and icons as well as link to your favorite multimedia on the internet or browse the already existing directory of publicly available content, in one sleek, fast and unified application!
Sports Devil on XBMC
SportsDevil gives you access to links for all the different kinds of sports. And I mean all! You will be shocked to see how many different varieties of sport that SportsDevil covers. It gives you several internet steaming sites to where you can view sporting events (it seems that it gets updated with new streaming sites every month or so).