As with many old Japanese cars, you can't go with blue book value. Sure, if you're just looking for one as transportation, but people who know what they are will pay more (and sell for more) than bluebook.
KBB, I agree. NADA Classic? It's been almost dead-on every time I check it. Admittedly it seems really low in this case, but if none ever come up for sale, it's tough to base the price on anything.
I find that NADA Classic is always a bit behind the curve, especially when it comes to Japanese cars. Like most classic car outlets, I'm sure their focus is on Euro and muscle and the J-tin is just an afterthought.
I'm not knocking them completely cause eventually they do catch up and it does take time to compile the data. But especially for some of the less common Japanese cars (Crown, Corona Mark II) they are dreadfully low.
Then again, I've been following mostly their Toyota prices for the past 10 years or so, and they might be more on the ball with Datsuns. For years after the AE86 began appreciating, they still had used A-to-B pricing...
How I long for a shit brown wagon.