From a visualization perspective, bar graphs are the last plot you should use. Bar graphs should only be used for counts or percentage of totals. To plot medians you should consider comparative boxplots, comparative histograms, or line-plots with medians and standard errors - something with distribution information included in the plot.
Comparing across categories could be very tough, even in the clothes example, some brands of the same item will hold price better than other brands. You may have to stick with directly comparable products.
Just no bar graphs, please!