I think the most disappointing case of choosing safety over money was sitting out a day of diving on our Indonesia trip because I came down with the cold that was making the rounds of the group. Luckily, it wasn't a bad cold, and it turned out I probably could have dived, and did so the next day and the rest of the trip. But I was a pretty new diver, and really didn't have any idea how to evaluate what my ears and sinuses were doing, so I played it safe. I lost one day of diving, and I don't know how to price that, because most likely, I will never get back there.
The hardest one was the last day of our wreck workshop. We had spent a day in the classroom, learning to run and follow line, and a day in shallow water, practicing our skills. The last day was to be experience dives, diving some real wrecks and having a chance to run some line. Although I hadn't, two of my classmates had gotten recreational trimix fills, because the wrecks were in the 100 fsw range. Unfortunately, the day dawned ugly, with high winds and rain. We called the instructor, who told us the charter hadn't canceled and the captain wanted to see how it went, so we drove to the dock. Even there, the captain didn't cancel (I realized later that if HE canceled, we got our money back; if we went out there and chose not to dive, he kept it.) All the way to the dive site, I kept looking at the three or four foot waves and the deep chocolate brown water, and thinking, "This is going to be an awful dive, and getting back on this boat in doubles is NOT going to be fun." We got there, and I looked around, and told the other guys in the class that I was very happy to wait for them, but I wasn't diving.
Whether it was politeness or not, I'll never know, but all three of the rest then decided not to dive, either. We went back to shore, where the instructors offered us another day of critical skills diving, if we wanted. We did. So my buddy, Kirk, burned off $50 worth of helium, running line in 30 feet of water.
Cost of the charter, as I recall, was $150 a person, and two tanks of trimix were wasted, so we had total losses of about $700.