I was browsing official forums several days ago and came across such thread there. Can't find it now, but it was very interesting for me. I totally agree, that generic ground mount without any vendors and without any useful utility shouldn't cost more, than 1K gold. So. What features or utility could make mount worth 2M gold/500$ for you?
Examples:
40 man raid bus
6 horse golden flying carriage with all possible vendors, Bank, AH, XMog, Void Storage, etc.