Comparison shopping is one of the important ingredients in electronic commerce, because it saves time and efforts of searching for product information and costs. However, most shopping malls still rely on the simple data such as price and other descriptive specifications, and cannot support the services of comparing the exact cost which requires rule based computation such as delivery cost. The comparison of delivery costs requires tailored computation because each bookstore has different free shipping rules, delivery options, and shipping rates. The purpose of this paper is to propose a rule based comparison shopping framework using XRML(eXtensible Rule Markup Language) approach. We propose the architecture, named ConsiderD, of maintaining rules in the comparison portal site to be consistent with its original pages. We experiment the benefit of using the rule based exact computation in comparison of book buying with the result by estimated average price such as BestWebBuy.com does. The result shows that providing the benefit of rule based comparison is significant and the hidden information such as delivery cost can be effectively processed with XRML framework.