In my experience of working for companies that justify overtime with discretionary bonuses, the bonus is always less than what I'd expect to earn if I was paid overtime.
What if the company was going to give you a bonus anyway (it's part of your employment contact), then asks you to work overtime. Will they pay a bigger bonus?
some firms offer a bonus. i guess that counts as free money way in the way that overtime counts as free time.
> the deal is an exchange of money for time
if that really was the deal, then you'd be paid hourly. i think most programmers exchanging results for money.