Allthough there are MMOs developed by single developers or 2-3 man teams.
It looks like Megahertz and I have different ideas of what a MMORPG is. "MM" stands for "massively multiplayer", which already implies a level of infrastructure that a single person cannot accomplish.
What's an example of a MMORPG built by a single person?
EDIT: From the Wikipedia page on MMORPGs:
The cost of developing a competitive commercial MMORPG title often exceeded $10 million by 2003. These projects require multiple disciplines within game design and development such as 3D modeling, 2D art, animation, user interfaces, client/server engineering, database architecture, and network infrastructure.
The only requirement to really qualify as an MMO is that the game supports a massive number of players playing together at the same time in a single game world, if you get rid of things such as realtime gameplay, content variation, etc it becomes quite doable even for a single person and hosting costs doesn't necessarily have to be that high. (a MMO where updates are sent/revieved once or twice per minute is still an MMO, and such infrequent updates pretty much eliminates the need for a complex server/network architecture. (If you have more players than a single server can handle at those rates you can just launch more game instances, rather than try to fit more players per instance)
Ofcourse, "Optimized 3D MMO" sort of suggest that the OP is trying to take on games like WoW head on.