Baseline values represent “all things being equal or normal” average values. Circumstances can easily change these, or the GM may override this, but the values represent a good starting point.
There are many things which can impact this, starting with availability. Economics can alter the normal baselines as well – taxation, artificial scarcity, controlled markets, war time policies, the ability to Haggle, etc. Real material scarcity can take an item’s value to nearly unlimited heights, especially if no new ones can be made. This may increase the value a hundredfold or even more, GMs may allow Haggling to influence prices as well.