For free? Who do you think has to cover the fuel costs, insurance, wear, tear and miscellaneous lube oils? You are having a laugh.:roll:
Of course you can do it for free. Join a line, help out, work your way up the metaphorical ladder to the position of driver/fireman/secondman and yes it costs you nothing, apart from getting filthy, getting up at the crack of dawn, explaining to your significant other that you are committed again this weekend.
Not forgetting that when all the (paying) passengers have gone home you still have to dispose of the loco after a long day. Oh, and then drive home.
Not ridiculous costs, just realistic.