If you just want a new intake manifold, you might check your local craigs list. Lots of deals on parts there.
If you want the new intake for an investment, offer him 50. If he tries the ' but this is made from unobtainium', ask how long he wants to sit on it....
The down side to collector parts is finding buyers that are concerned with date codes.
I have a complete "A" code engine with buddy bar 'cobra' valve covers that needs a rebuild in my garage. Most folks think it's only worth a couple hundred bucks as a 'core'.
I think it's worth more, but then I don't know anybody who is willing to pay what I think it's worth. I actually don't want to sell it, because I think the motor and the carb and the valve covers with all the aluminum tags make it 'unobtainium'.