Uhh, local place here has a pile of classics, color classics, SEs and SE30s and not one costs more than $75 and they're all working, with software.
Do they have the original box, packing materials? I wouldn't exactly call it rare but if it does work and has all the original included items in good condition, $400 isn't out of line. Personally, I would never pay that but there are those that would.
There are people that collect old computers and having the original box/disks is what they look for.
-KeithP