UK ONLY: Who to go to, and how much does it cost to set up a Wi-Fi system?

I use BT at the moment for all my broadband, wifi and phone calls, though I'm thinking of switching to another provider. BT is okay though, and at least the customer service offers a 'human being' to talk to if you have any problems. I am considering moving to Virgin, purely for cost reasons, though customer services is not the best, the savings are considerable.