The issue of pro-rata expense belongs to the private pilot. The original poster is a commercially certificated pilot and regardless of work laws or authorizations in the United States, is not prevented from being compensated as a commercial pilot.

The FAA has long held in legal interpretation that the logging of flight time represents compensation, not the flight time itself. In this case, it's irrelevant.

So far as regards the original poster, whether it's a troll post or sincere, you shall find little support or sympathy in offering free services. To do so lowers the bar for everyone, regardless of whether work is taken away from others or not. It may well be that whatever flying you do for free would not have been done by another pilot, or in other words, it's possible that you're not preventing a working pilot from receiving compensation or taking his job. That does not alter the fact that by offering to fly for free you're denigrating the concept of the paid, or commercial pilot. Those who do so are seen very unfavorably by those whose livelihood is dedicated to the betterment of the industry.

In short, by making the offer, you've become part of the problem. You'd do well to retract it.