1. A recommendation system for generating recommendations of alternative unique items, the recommendation system comprising: an items information database configured to store data relating to unique items; a penalty computation engine configured to calculate a dissimilarity penalty, the dissimilarity penalty at least partially generated based on a magnitude of dissimilarity between a selected item and an alternative item, the penalty computation engine comprising: a customizations filter configured to calculate a customization score, the customization score representing an estimated preference impact of a difference between at least one customization attribute of the selected item and at least one customization attribute of the alternative item; a condition filter configured to calculate a condition score, the condition score representing an estimated preference impact of a difference between at least one condition attribute of the selected item and at least one condition attribute of the alternative item; wherein data representing the at least one customization attribute and the at least one condition attribute of the alternative item is configured to be stored in the items information database; and a dissimilarity penalty calculator configured to generate the dissimilarity penalty by combining at least the customization score and the condition score; a recommendation compilation engine configured to generate a recommendation of alternative unique items, wherein the recommendation compilation engine is configured to electronically communicate with the penalty computation engine to calculate dissimilarity penalties for each of a plurality of alternative unique items, the recommendation of alternative unique items comprising a ranking of at least a portion of the plurality of alternative unique items, the ranking based at least partially on the calculated dissimilarity penalties; and one or more computers configured to operate the recommendation compilation engine, wherein the one or more computers comprises a computer processor and an electronic storage medium.