"Flash prices" are essentially short-term discounts or promotional offers that are designed to create a sense of urgency or excitement among customers. Businesses often use these flash prices to attract more customers or to boost sales during slow periods. In terms of synonyms, you could consider using phrases such as "limited time offers", "special deals", "price drops", or "flash sales". Each of these phrases indicate that the prices are only available for a short period of time or under certain conditions, just like flash prices. Regardless of the word you use, they all serve the same purpose of attracting customers to your business with offers they can't refuse.