Awe, that's easy! If a 3/4 goes for $2K, a half should be about $1333.00. Much abliged!
Seriously, those are kind of not in high demand, but not in big supply either. Offer 500 bucks and see what happens.
Any reason you want half a bass instead of a whole one, I mean 3/4 of one? Wait, Kay never made a 4/4 bass did they? So you're set on a Kay? Well OK. Cool basses. Don't worry, I have a 4/4 and people still look it and say, "What a nice cello...."
It all depends on the condition though. Look it over very carefully. Make sure the pegbox and neck join are solid and thump it all over to make sure it's not de-laminating anywhere. If it's all there, it's an OK bass for a few bucks.