Abstract: A web-based online store user interface enables custom configuration of a computer system according to identification of a user belonging to a prescribed customer set. A configurator configures a computer system with options selected according to a desired user input, and presents the options and a respective pricing for each option on a configurator web page. A database dynamically supplies configuration options to the configurator in accordance with identification of the user belonging to the customer set. A cart temporarily stores a configured computer system and presents the configured system on a cart web page. Lastly, an interactive upsell advisor operatively couples to the configurator, the database, and the cart, wherein the advisor selectively provides an upsell recommendation to the cart as a user selectable cart option on the cart web page, further as a function of the customer set, the configured computer system, and upsell advisor business rules.