I sold one of my two for about $650 on Ebay within the last two years. It was in excellent condition and included the original Alvarez hardshell case. Given the current economy, it's hard to say what you could sell one for. Mine have built-in transducer pickups beneath the bridge, as many do (if you can put a 1/4 RCA plug into the strap button, you're in business; it's passive). If I were to be selling it again today, I would expect anything from $450 to $800, depending on demand. These Alvarez acoustics of this era are excellent instruments of top-notch materials, built by master craftsmen in Japan under the supervision of the much acclaimed Yairi family.
I am thinking anywhere between $300-$500 depending on the condition. Although very cool and unique, the overall market demand for a 9-string acoustic is not very high. Don't let the word "rare" ever become synonymous with meaning "expensive".
I have one for sale at $980. Beautiful. No damage when i bought it but had expert luthier upgrade with a bridge doctor, new custom bone intonated saddle and new grover deluxe period-correct tuners. I've seen them anywhere between $600 and $1800. Kind of a buyers/sellers market...whatever someone is willing to pay. I think a fair price (for a good one!) is $800-$1000
Mint condition is around 800. 1978 was last year mfg.
It depends on what condition it is in, I own the same model Electric acoustic Alvarez Model # 5082N serial number 614845, It was appraised at $2,250 in mint condition.