I'm taking an intro to data visualization class, but I don't have a strong foundation in statistics.
For now I'm trying to do something basic with bar graphs.
I basically want to plot the median price of two types of products. I'm trying to see how much the condition of an item affects its price and comparing it with another type of product.
median price (normalized in some way) | | | A B | B   |    | A    |_________________ condition (2 for now) used new
A is product type A. Let's say clothing for example. B is product type B. Let this one be guitar amps.
A typical piece of clothing can sell from \$20 to \$300. A typical new amp can sell from \$100 to the thousands. As you can see, these products have wildly different price ranges.
For some products, the price between used and new drops only a little, because wear and tear doesn't matter much. For others (like clothing or cars), the price drops a lot.
If I just plot the actual median price, then only the comparison between used and new of the same product type would be useful. It would be hard to compare with the other category.
What sort of calculations can I apply to the data in order to make this useful for comparisons? Am I approaching this in the wrong way?
Data-wise, right now I have access to the individual prices of items with a specific selling condition.
I'd appreciate any help.