A fully Internet-connected business environment is subject to frequent changes. To ordinary customers, online shopping under such a dynamic environment can be frustrating. We propose a new E-commerce service called the CIGMA to assist online customers under such an environment. The CIGMA provides catalog comparison and purchase mediation services over multiple shopping sites for ordinary online customers. The service is based on up-to-date information by reflecting the frequent changes in catalog information instantaneously. It also matches the desire of online customers for fast response. This paper describes the CIGMA along with its architecture and the implementation of a working prototype.