A lot of questions related to how much x costs or what is the price of x could be seen a valid short term only. Pricing depends on your world, the time of day, if there's events going on, the amount of players etc. It just completely varies.
My suggestion, because these questions are really helpful for the moment their asked maybe we can have a tag that is meant specifically for these questions? Or a category for these questions would be nice even like a market category (I know we already have that tag but by category I know questions are listed under recent, hot, etc) Maybe the tag can be listed under price? That way players can easily go back and see if they need to edit the answer.
Or maybe for players viewing the question we can have a little warning that says pricing can vary based on numerous factors blabla just incase the answers get outdated?