Is there a native terminal in OS X, without having to load the desktop, window manager, etc?
I don't think Single User Mode is really what you want.

A better idea is to use a console login.

To do this, first you have the login window set to show “Name and Password”:



Then you can login as ">console" as the username (no password) and get a terminal prompt.

It's not very pretty, but it's handy if you need it.