Before you buy anything
A few things worth knowing first
Rent for your first three to five sessions before buying anything. Most surf schools and beach shops have rentals for $15-25/session. You won't know what size board you want, what wetsuit thickness you need, or whether surfing will actually stick until you've stood on a wave. The cost of renting wrong is $25. The cost of buying wrong is $400.
Bigger board equals more waves — every time. When choosing a board, resist the pull toward shorter, more 'professional'-looking shapes. Volume (measured in liters) equals float, float equals wave-catching, wave-catching equals actually standing up. A 9-foot foam board catches ten times the waves a 7-foot board catches. This is not a trade-off. Bigger is just better for the first six months.
Foam boards are not for beginners only — the white foam softop is the industry standard beginner board for a reason. It's safe (soft rails won't crack your skull when the board hits you, which will happen), buoyant, and stable. Plenty of intermediate and even advanced surfers ride foam boards. Avoid secondhand fiberglass boards for your first six months unless you have an experienced surfer helping you pick.