It used to be possible to create your character on another world and buy a server transfer to get into high pop worlds even though they were locked. I don't know if this is still a thing, but if it is, it's gonna cost money.
Also, there's a reason those servers are locked, look at super high population servers, they have hour long queue times to even get into the game and suffer from severe lag at times. Not even starting on the housing situation on those worlds.