I have a few days to decide, since there might be others interested as well
Anyway, I'd avoid pre-1985 Japanese pianos. Their built for the climate in Japan, and are not suitable for the US.
Is this a private seller or a dealer?
Have you had your independent piano tech evaluate the instrument? Such person can inform you on the condition of the piano and also their opinion on a reasonable price. Look at the serial number, there should be a letter before it. This letter is the version / revision of the C3 model. There have been design changes between versions.
This may be a selling strategy. Make sure you have a counter offer prepared with a date of your own. A tech's evaluation can help you determine your offer. Be prepared to "show" no interest and walk away, especially if you have found a connection with the instrument.
My personal take on used Yamaha C3's: they can be excellent instruments if voiced and regulated well. IMO a well prepped, broken-in used C3 can outshine a brand new stock C3. This opinion may come with a little bias as I have a used C3, that does not carry the typical Yamaha sound found on new instruments. With a good tech, it is possible to bring the sound closer to an S series.
WAY too much money for that piano! That much money will get you one 20 years newer.Anyway, I'd avoid pre-1985 Japanese pianos. Their built for the climate in Japan, and are not suitable for the US.That's not to knock Japanese quality. They just didn't build them for US climate until the mid 1980s.
Regarding the manufacture of Japanese pianos prior to the 1980s ... Larry Fine's "Piano Book" and his publication at pianobuyer.com talk about this. It's widely known in the industry. Check it out.