Fred would like to know the cheapest way to promote his band's website. Leo says giving away music is a great option. Participate on Facebook, Twitter and Google+. SoundCloud is a great social sharing site for music. Giving away music builds a fan base and that should be job one. If he can build a fanbase of 1,000 fans, they'll take care of the rest and he can then begin to sell his music online.
Check out how others are doing it. Like Umphreys McGee, who gave away their music and did cool things like set up fans to be able to listen to the raw feed from the sound board, selling concert shows on USB keys, and other out of the box options. He should start with SoundCloud though.