They did that with magic items and you see the kerfluffle it caused.What? You mean that D&D is a vast oversimplification of reality and it's meaningless to try to analyze specific details? Sacrilege!
Maybe with the next edition, they' just specify that you need 2 ounces* of ruby dust (specifically made from AAA grade rubies, not that industrial quality crap) and then let the DM decide how much that would cost in their campaign world. Much more realistic!
*None of this metric stuff in D&D, obviously the metric system hadn't been invented yet in the timeframe of the game.