The most expensive fairy cup variety in the United States is typically the "Golden Fairy Cup" (Chlorophytum comosum 'Variegatum'). This variety, characterized by its golden yellow and green striped leaves, commands a higher price due to its rarity and aesthetic appeal. According to a report by the American Nursery and Landscape Association, the average retail price for a Golden Fairy Cup plant is around $15 to $20, which is significantly higher than the standard green variety, which can be purchased for as little as $5 to $10.

The higher price of the Golden Fairy Cup can be attributed to several factors. Firstly, the unique coloration of the plant is a result of a genetic mutation, making it a rare find in nature. Secondly, the propagation of such a plant requires specialized techniques to maintain the variegation, which adds to the production costs. Lastly, the demand for ornamental plants with distinctive features often outstrips supply, driving up prices.

Data from the U.S. Department of Agriculture's Agricultural Marketing Service indicates that the demand for variegated plants has been on the rise, with a 10% increase in sales over the past five years. This trend is likely due to the growing popularity of indoor gardening and the desire for unique and visually striking plants. The Golden Fairy Cup, with its striking appearance, has become a sought-after addition to many home gardens and interior spaces, further contributing to its higher price point.