I have one, there were less than 200 made from what I've found. Not much info out there as you've seen. It's a collector's item, I'd keep it.
It's a cat-rig, free standing carbon fiber mast, furling main, inboard electric engine with solar charging... Hoyt boom, inspired the Alerion 19 (people like big boats on this site might recognize that name). Perfect trailer sailor for local lakes. Main furled around free standing boom, just step and launch. She's a pudgy little girl, 13' long and 6' wide, not a racer.
I traded an SJ21 valued at about $4K, the Expo was in very rough shape. If anything happened to her I'd drive several hours and pay twice+ that to replace. "Fair price" for one in decent shape is probably $5K, which is why I suggest keeping it. It's worth far more.
Expo Solar Sailer