This was generally the case in this business for its entire history: prices were not publicly stated at all. There was no page on the ULA homepage with a price. SpaceX was the first company which did put a definite price on their official website, instead of asking potential customers to give them a call. In years past, this did not stop people interested in the topic from digging for data and discovering approximate prices of launches. One source is launch costs for government payloads, such as NASA planetary probes. By looking at various data, it was determined that Delta IV Heavy costs $400m a pop. Atlas V used to start at around $180m in the least powerful configuration. Now they are forced by competition to lower the costs and now they say the price is $109 million for the smallest configuration (Atlas 401) up to $153 million for Atlas 551. They also followed SpaceX example and set up a website with pricing information (RocketBuilder). It's amazing what happens when you suddenly have a competitor.