God, I don't even want to think about it.
This month alone I have spent over 700 US dollars. Most of it in acquiring original documentation on the original paper.
Books? I spent about 200 on books this month which is what I have been averaging with a spike like this month every 2-3 months.
That does not include gas, food, hotels, etc.. when traveling to archives/museums for research either.
Expensive to research a book. When you see guys post documentation, like Henning, Guppy, F4UDOA, and others, be sure to thank them. They are niether free nor cheap.
All the best,
Crumpp