When the BMAH launched back in MOP people were bidding really high on T3, even on medium pop servers. You had people like me going into that expac with 5+ mil gold, we finally had something to spend it on.
I guess it also had to do with getting the first peice of dreadnaught in every slot to pop up on my server. Not sure what i paid exactly but i'd guestimate 1,5-2 mil. This wasn't even a big server.