Mouthpieces (like everything else) are worth whatever somebody wants to pay. I bought my vintage Soloist E -- in near-mint condition -- for forty bucks from somebody who didn't really know what they were letting go. At the same time, Sarge over at World Wide Sax has vintage Soloist C* in pretty good condition for $199.
No matter how much it's worth, though, these pieces are awesome, and I have to agree with Daigle65: it might not be the best idea for your son to use it in school. You'd be surprised what kind of madness takes place in your average middle school band room.
No matter how much it's worth, though, these pieces are awesome, and I have to agree with Daigle65: it might not be the best idea for your son to use it in school. You'd be surprised what kind of madness takes place in your average middle school band room.