Let's start by separating 'Freeview', 'Freesat', 'Freesat From Sky' and generic 'Free To Air' satellite reception.
Freeview is an entirely terrestrial service. Without a functioning aerial you can't receive it. End of story.
Freesat requires a special set-top box, which will cost you around £30 at Argos (but you can continue to use your existing dish):
http://www.freesat.co.uk/
Freesat From Sky (which, confusingly, isn't the same thing!) can use your old Sky box with a special card in it (which Sky will sell you for a one-off payment of £25).
http://www.sky.com/shop/freesat/home/
(NB: Ignore the prices on that page. The bit about just paying £25, and using your existing equipment, is on the FAQs page).
However both of those services simply receive the 'Free To Air' transmissions from a group of satellites collectively known, from their location, as "28 degrees east". All that you get in addition is the electronic programme guide provided by either Freesat or Freesat From Sky, as well as access to some interactive services if you choose Freesat From Sky. If you can do without those things, you can simply continue using your old Sky box (with the expired card still in it) and you'll still receive all of the channels listed in my first (Wikipedia) link above.
Chris