great idea, but i dont think it will really help.
The lack of players makes items rare to find, since no one is on to sell them, so players having a specific item are free to make it at the price they want, and you either take it or leave it (because if you really need it you will buy it)
in short, there is no "competiton" between sellers, therefor a player can make prices by themselves
But it can help new players to no get scammed (by not buying a 20m item for 200m for example) so
Edit : it will also be shit ton of work since no data can be collected about prices due to lack of players, and the prices arent really stable so it needs to be updated once in a while