It depends on the local market. I'd say at least $1700. I saw one sell on ebay for more than $3,000 last year.
The S models are worth more than the Ms and the Ms more than the Cs.
Is the hard case an anvil type or a fiberglass trunk? A flight case has value as well.
If you have the serial # you can find the year of manufacture here:
http://www.kaybass.com/mnfgdates.htm