A strong advantage of buying products in on-line shops is a wide choice of alternatives. From customers' point of view it is good to know where to go in order to buy all required products – the entire shopping list – at the best possible price. Making such decisions requires three elements: information where the required products are available, access to price lists in considered shops, and finally, specialized analytical tool that could find the minimal subset of shops where all the products from the customers’ shopping list could be bought at the lowest price. In the paper we propose the mini-mini algorithm and describe a web-based customer assistance system dedicated to pharmacy shopping that helps customers find shops in a geographically defined range where the entire shopping list could be realized at the best price total. The same algorithms might be applied to other applications optimizing Internet shopping where the cost of basket delivery is negligible when compared to product prices.