Ok, lets start with some ground rules…
1.) The question has nothing to do what you do with them afterwards.
2.) The question has nothing to with Plexing or paying RL cash for subs.
3.) The question is only in relation to actually gathering/acquiring minerals beyond initial investment costs to be able to gather them. (think really hard about this part.)
4.) any notions of opportunity cost have no place here, see point 1 above.
I will personally give the person that can without a doubt prove minerals are not free to gather 1 Billion ISK.
So lets begin…
How are minerals not Free?