I know from being there long enough to know that the 3rd clothing item (the much more expensive one) was recently added a few months back because for a very long time there was a lack of new strange stone reward. So I guess the idea was that many people had an excess of stones / they just decided to add 1 item with crazy price so people won't ask for new things again for a while lol. So I'm guessing maybe the other item prices are also the result of something similar where one got implemented first and one got added in later.