um.
the SR71 is a single-seat ramjet-powered mach5 spy plane.
IIRC:
the pilot is in the pilot's seat for the entire flight.
there is no other seat - the cabin being quite small and cramped and spartan
there is thus no separate toilet requiring a $500 seat
presumably the pilot of an SR71 did/does what all other pilots must: fills his suit when the need arises.
Does the suit cost $500?
um.
The SR-71 is a two seater.
You are correct in that it has no lavatory- but that doesn't stop old Lockheed rumors like...
http://www.worldpolicy.org/projects/arms/updates/nmdtitle.htm