Assuming you know the right questions to ask. Most people don't know what they don't know. I've tried this. I'd prefer to pay a small amount to read the book.
Is that really that much of a barrier? Off the top of my head: you could start with a prompt like "write a summary of book XYZ, followed by a summary of each chapter". Then dive deeper into each one from there using the same prompt recursively, etc.
Yes, it’s a tremendous barrier, which is why academic fields tend to have introductions or surveys of the domain, stepwise instruction, with more in-depth or specialist knowledge being premised on having this understanding. I feel like this should be obvious to everyone? Did your education not follow such a progression?