Maybe $50-$100 in today's market for vintage classicals.
Stalk eBay and Craigslist and look at comparables to your vintage. Most of the Japanese guitars of this vintage sell very low, depending on the maker. Yairi go way higher. I think a lot of this vintage are laminate and were originally inexpensive, and many could have neck bows or need a reset. You might want to put a new set of strings on it, if the neck is straight, and try playing it.