It does not sound unethical, actually it sounds like normal market dynamics (adjusting your prices over time), and airline companies used to do that all the tim

It does not sound unethical, actually it sounds like normal market dynamics (adjusting your prices over time), and airline companies used to do that all the time and even Amazon experimented it. However if your customers notice the price for a good/service changes without logical explanation, they can resent your company and start complaining (publicly or not) about the unfairness of your prices. You might be interested in listening to an episode of Planet Money named "The Birth And Death Of The Price Tag" (https://www.npr.org/sections/money/2015/06/17/415287577/episode-633-the-birth-and-death-of-the-price-tag https://www.npr.org/sections/money/2015/06/17/415287577/epis...).