Yea thats a good idea maybe not 2 mil because thats a bit excessive, but maybe 500k -1mil and like i said if people abuse it its easily proven and sanctionable
Or, to avoid chat spam, it could be hidden and only accessible for whoever wants to see it. Something like this:
/set advertmsg Miner in Tau-23, at Java, selling 2500 niobium ore for 30.000.000
The message appears in system only when it's made. After that, if a trader in Kyushu is looking for something, he can:
st advertmsgs
and choose from a list that only he can see. How about that?