An affordable book is called "Japanese Rifles of World War II" by Duncan O. McCollum.
It's an oversized paperback and only 61 pages so it's pretty basic. Discusses the major models, the markings, the many changes over the production runs. Good to have even if you later find a more expensive volume. Should be able to find a copy pretty easy online or on ebay.
After that, the price seems to go through the roof to well over $100 for any book dealing with Japanese rifles. I've never seen a copy in person so I can't comment on their value to the collector.
