Modifiers like "Chipped", "Bent", "Cracked", "Rusty", and all the rest that decrease effectiveness also drop the price by a certain percentage. Similarly, "Thick", "Reinforced", "Heavy", "Balanced", "Hardened", and other modifiers that increase effectiveness also increase the price by a certain percentage.
This is why (for example) a Reinforced Type X Shield costs more than a standard Type Y shield, even though they both give approximately the same defensive value.