If you've just got a Sky box, without a valid viewing card, you'll just get the 'Free to Air' channels. If you've got a Sky box with a 'FreeSat' card in it, you'll get a much wider choice, including all of the 'Free to View' channels. See my post here (together with the links) for an explanation of what I'm on about:
http://www.theanswerbank.co.uk/Technology/Ques tion444482.html
So you really should be seeking to acquire both a Sky box and a FreeSat card. Sky will install a completely new system for you (i.e. dish, cabling, box & FreeSat card) for �150. (The link is in the post referred to above). That's a one-off fee; there's no subscription involved.
Alternatively (if you're really sure that your dish and cabling are OK), you can buy a replacement Sky box cheaply on eBay. (Read the description carefully to check that it includes the remote control and, of course, look for good feedback from buyers). The box might cost you around �20. Then you just need a FreeSat card, which Sky will sell you for another �20. (As stated above, there's no subscription involved)
Chris