Below are Yamaha CS-80 synths and parts that are either on the market or have sold. My purpose with this post is to follow the market and keep a registry of sorts. I’ll try and keep this post up to date as CS-80s are listed and then sell. Maybe someday I’ll get one!
Update July 3, 2021: Right now on Reverb you can buy an original CS-80 workshop / service manual for $569.67. The odd asking price is probably because the listing is out of London UK and in British Pounds. Like the legs that sold a few days ago, I wonder if this is a lot of money for a manual, or a good deal for an item that helps complete a CS-80 package. I admit, I am the sort who buys original manuals for all my Synthesizers and doesn’t give them up when if I sell the synth.
Something to think about: they sold about 800 CS-80s. Each of them would have come with an Owners / Users Manual – and Yamaha probably printed off extras for owners who lost them or whatever. Service manuals on the other hand did not come with a synth when it was new. They were deployed to the global network of Yamaha service centers and techs. There could be thousands of CS-80 service manuals floating around for the handful of CS-80s ever made. To test this theory see how many GX-1 service manuals are out there for the 10 or so examples of that synth they ever made.

Update July 1, 2021: Someone spent $3000 on a stand and the rare leg carrying case for a CS-80! Seems strange, but if you have a CS-80 these days and your value is pushing whatever you are brave enough to ask, you probably need these if your example didn’t come with them.

Update 5/15/2013: CS-80 number 1259 is on eBay right now. Used by Little Feat, not sure anyone buying a CS-80 is going to care about this. Asking price is $17,999!

Update 8/16/11: The $17,999 CS-80 from Perfect Circuit has sold for asking price. A new record?
I keep an eye on the search term ‘Yamaha CS*’ since I have a CS-50 and am always looking for parts to squirrel away. Tonight I was surprised to see there is a CS-80 arms race going on. What’s all the fuss? Check out some Vangelis CS-80 demo’s on YouTube and you’ll see.
First up is this guy from Perfect Circuit Audio for $17,999 out of Southern California.

Someone’s got some solid Photoshop skills. That is a mighty fine looking keyboard. $17,999 is the Buy it Now.
Next is this fellow out of New York -15 minutes from Manhattan to be exact. It has been fitted with Midi which is quite a job on a monster like this.

Comes with 3 pedals, the legs, top cover etc. Oh, and only $19,900. Local pick up only.
Then we have this dusty relic for sale by a seller that specializes in odd stuff.

$18,000 is the ask. Looking at it I’m thinking this is a $10K-ish instrument since it’s untested and sold as-is.
I think it all started because of this guy. Also a Midi modified machine. Also in Southern California.

Yep, this sold on eBay for $12,500. A seeming bargain.
There is a chucklehead having a laugh right now… he put up 6+ different listings for the same (likely nonexistent) CS 80 for a BIN (offsite) of $1800. LOL.
After three years of restoration…….the “nonexistent” unit will be back on Ebay next week. And yes….this chucklehead is laughing at the return I am expecting after getting the unit for free a few years ago.
There is another synth on ebay right now in London, for £18k. Seems fairly resonable price?