fish sell for a wide variety of prices, depending on demand at the time.
I bought a R5L for $650 shipped with brand new strings a few months ago -- it had sat on the classifieds on another forum for a few weeks, going down in price, until I couldn't take the GAS any more. It's one of the first fivers, and one of the very finest basses I've ever played -- worth every penny, and then some. Had I known how good it was earlier, I would have gladly paid much more for it.
I also bought a Reverend BH5, which was their top of the line five-string, and has been out of production longer, for $1k. However, it was in the Lava Swirl finish, and I think there is some more demand for those. It's one hell of a bass, as well -- getting about equal playing time with my $2k+ Sadowsky.
Both of them came with the case, a big bonus.
I'd say that the Green JJ in question is worth $700-800, easy. It's in a rare color, is a low number, signed by Joe, and comes with the case. Four-stringers sometimes go for more than fivers, since the old-school crowd who is more likely to buy a fish is also probably more likely to be a four-string player, so the demand may be higher.
I would also expect to see prices on used 'fish rise in the next few years, which is one of the reasons I jumped on the BH5. Reverend afficianados like me are not likely to sell any of theirs any time soon, since production of more seems unlikely.
Best of luck. I had an eye on the auction, but everyone's watching it, and my wife would have my head on a platter if I reeled in another 'fish. The green one is mighty nice, IMO.
Bart