How much is the bus fare of an airconditioned bus travelling from Bangkok to the Cambodian border?

audrey asked: Our trip originates from Bangkok via bus. How much is the bus fare (airconditioned) on bus plying to the Cambodian border. Do we need to buy the tickets prior to travelling or can we just go to the bus station and get the tickets there and ride the bus or there must be prior arrangement. Where can we buy the bus ticket.Victoria