FG-410 Price Spread!?

Hi, I’m new to the group and to Yamaha guitars. I picked up FG-410 with some damage to use as my camping guitar. I can easily repair it with a little glue and a clamp. In doing my research I see that they are priced as low as $150 or so and well over $700. I know condition, quality of case, but are the build years or vintage making them that much more valuable. How do I get a reasonable idea for one built in ‘75 in good condition? As long as it sounds plays well, it’s in good condition. Haha. I’m gifting it to my nephew. I just want to let him know what it be worth without the damage. Thanks. I hope people don’t ask this question all the time and I hope theirs a short answer. Haha.