The Lunar books (if they're the official Working Designs ones) are at least $30 a pop, I think the Eternal Blue one is going for $80+.
Even some recent ones have really good collector value, Star Ocean: Second Evolution is $50+ and the Future Press Bayonetta one is like $250+, I've seen it go for more than a thousand more than once.
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I chose poorly. Black Turtle chose wisely.