Advantages: Carbon Fibre is strong, lightweight, relatively cheap and easy to form into complex shapes.
Disadvantages: Not great on impact damage, failures can be sudden/don't always manifest themselves in a visible way.
Misconceptions: Carbon fibre is fragile, carbon fibre is always lighter than other materials, carbon fibre always produces a stiff frame.
Brands: Most well known brands have carbon framed bikes in their ranges.
Price: can vary massively dependent on brand. A lot of frames are pretty generic made in trusted Chinese factories. Very few are bespoke and made by the well known manufacturer.
I have just passed 50,000 km on my road frame it is a generic Chinese frame from a known Chinese brand. It cost about £350 to £400 iirc. I have raced it, crashed it mutliple times and it is still going strong. It weighs about 7.5kg when built up with reasonable components. Anecdotally I would say you don't need to spend a fotrtune to get a good, lightweight bike if you don't get too hung up about brand names.