The reference is an obviously cut and pasted article from Wikipedia?

This is provenance nowadays? I really don't think so.
The expert, Randy May, says "it is as close to 'original' as has ever existed" without giving a single piece of evidence to that effect. He further states, "I believ (sic) it very likely that what you say about 6 of them ever being produced is probable but undocumentable." In other words, it's either your client or you who says that only 6 were made in the manner you describe. Again, evidence here, please.
It is an interesting artifact but is only worth what you can get in an auction, nothing more. You haven't even said if this is the movie or the TV version of the ship. The expert, Randy May, implies it is the TV version but I don't trust him. Tell me, has he even seen this portfolio, or is he just an
Internet expert?
This appraisal isn't even worth the electrons that make it up.
You want a real estimate and opinion on this piece, CLLCTR5? Go over to Trek Art. Post multiple pictures of this blueprint, not one small snippet. Give a full inventory of what's inside the covers. Talk to them about how your client came in possesion of this. Get opinions from real experts, not a guy who is proud of the baseballs he has appraised.