How valuable are certain interface features to their users? How can users' demand for features be quantified? To address these questions, users' demand curve for the sorting feature was elicited in a controlled experiment, using personal finance as the user context. Users made ten rounds of investment allocation across up to 77 possible funds, thus encountering choice overload, typical of many online environments. Users were rewarded for positive investment returns. To overcome choice overload, users could sort the alternatives based on product attributes (fees, category, fund name, past performance). To elicit their demand for sorting, the experimental design enabled users to forgo 0%-9% of their reward in return for activating the sorting feature. The elicited downward sloping demand curve suggests a curvilinear relationship between sorting use and cost. More broadly, the study offers a way to quantify user demand of UI features, and a basis for comparison between features.