Actual example of financial unavailability. One of my wife's favorite kids books, "The 14 bears in summer and winter" was out of print for years. It was a collector classic and was fetching upwards of $300 in the secondary market. We didn't buy a copy, we didn't "pirate" one either.
The publisher saw the high price as proof there was still a demand for the book and produced another printing. We paid full price for it, around 15 bucks, I think. It's a cute book, I'm glad I have it, I wouldn't have wanted to pay $300 for it, though.
One could make the case that if everyone could just "pirate" the book because it was financially unavailable, then the publisher would never bother doing a re-issue.
More broadly, I think that respecting copyright holders (and the rule of law) means that sometimes you don't get exactly what you want exactly when you want it.