Joe, several factors combine to inflate book prices. Printing costs are up, so dealers inflate the price of older editions- people will pay more so dealers put the price up. There are a lot more literate people that there were before WW2. Many books were in smaller editions then, and current demand kicks the prices up. The population has also grown dramatically. Book publishers hate small reprint editions, even if they hold the copyright. Even if there is a small, steady demand, the profit margin is small.
I have collected western history and don't find it unusual for a title issued in 1960 to bring 20 times or more its issue price now.
Libraries are becoming less useful. Librarians hate books that are consulted only occasionally, so they toss them out. Also, anything more than 20 years old is suspect. This means that if I want an older book, my only option is to purchase it. This, again, adds to the demand.