You know the clich?, it's worth what someone will pay. Of course you can research the internets and see what various individuals and stores are asking for a similar instrument. Often what people are asking is not what they end up selling for though.
On Ebay you can perform searches that specify completed listing only. This is very informative as it tells you the prices that items did and did not sell for. When you have something that is more specific, like say, a 5 string Europa, you don't get very many examples to compare.
I can tell you that last year, I purchased a used 1992 five string Europa, with a beautiful redwood burl top, and new frets. Except for some finish checking where the belly rubbed the back of the instrument, it is in fine shape. I paid $2500 and feel like I got a very fair deal, no regrets.
With Alembics, there are so many variables with respect to woods, that even within a particular body style or electronics designation, there can be wide range of potential values.
If you really want to find out how much it's worth, list it on a site like this one, or Talkbass.com, at a high price, and ask for offers. See what you get. Or you can always be bold, and put it up on ebay, starting at $1 with a no reserve auction. That will tell you what it's worth, in that particular 10 day period, to the potential buyers that you reach.
Good luck, James
