Slingboxes are great, however, the fuller explanation is that you have to have a connection (let's say Sky in the UK) to which you're going to connect one 'half' of the Slingbox. You then have the 'other half' linked via the internet, so are remotely controlling your 'home' tv service. Cost of course is the actual tv content (in this example, Sky), and you need to have a decent internet connection as you're 'streaming' your link.
As with any of these 'streaming' services, there is of course the time differential to consider.