You can buy the cheapest franchise for about £500 but the normal package is £1000.
I'm not sure what you get for each but I did look into this very recently.
I know you have to pay for room hire, advertising, leaflets, posters etc etc and you do have to sell sell sell. This was the part that put me off. I can do the stand up and talk and help bit but I really don't like the promo side of SW.
You have to go to a fair few meetings which you have to pay for your own travel etc.
They tell you everything at the Info meeting so it's well worth going along to.