This paper addresses the interpretable estimation of price bounds within the context of price optimization. In recent years, price optimization methods have become indispensable for maximizing revenues and profits. However, effectively applying these methods to real-world pricing operations remains a significant challenge. It is crucial for operators, who are responsible for setting prices, to utilize reasonable price bounds that are not only interpretable but also acceptable. Despite this necessity, most studies assume that price bounds are given constant values, and few have explored the reasonable determination of these bounds. In response, we propose a comprehensive framework for determining price bounds, which includes both the estimation and adjustment of these bounds. Specifically, we first estimate the price bounds using three distinct approaches based on historical pricing data. We then adjust the estimated price bounds by solving an optimization problem that incorporates shape constraints. This method allows for the implementation of price optimization under practical and reasonable price bounds, suitable for real-world applications. We report the effectiveness of our proposed method through numerical experiments conducted with historical pricing data from actual services.