Robert Fletcher Spock Kolinahr costume from Star Trek: The Motion Picture. Though this piece is iconic and rare I think it's hardly worth the estimated $30,000-$50,000. Spock costumes are few and far between but the distressed nature of this one and the fact that it is seen on screen for less than 5 minutes reduce its value. I'd say a more reasonable price for this might be $10,000-$15,000. We'll see how it does at the auction!
UPDATE: Unsurprisingly, the Spock costume was passed over at auction this evening. $30,000 is a ridiculous opening bid for this piece. Though there was healthy bidding on some of the Star Trek items in this auction a great many were passed over. The opening bid prices were simply too high. The John Eaves concept art sold for a solid $700.