I suspect that threshold has more to do with the average level of wealth of my cohort than with our willingness to signal honesty.

I would simply not trust the person making the offer for 100$. How do they make the consequences go away? Surely that costs at least a few thousand, assuming we're in a stable country. So why pay me so little? Besides the risk though, I don't see why murder should be expensive. It's not exactly complicated, assuming an unsuspecting civilian target. 100$ seems like a reasonable sum for the amount of work.