I have both a yellow assessor and a blue assessor...great fish! They are two of my favorites, and yes it took me forever to find them as well. But they have been very hardy and completely reef safe.
Scott gave me my assessors when he closed down Aquarium World. They were in his display tanks, so he just let me have them (I was literally jumping up and down with joy!) So I have no idea what they cost, but they are very difficult to find.
If I recall correctly, ORA was able to breed them and raise the young, but lost their breeding pairs in the hurricanes. I think that while it is possible to captive breed them, it is very difficult, so they haven't been successful in reestablishing breeding pairs...yet.
Oh, and don't worry if you see him swimming upside down...they do that. They are just goofy fish, I guess.
Congratulations and enjoy...you got yourself an awesome fish!