score:4
It should be possible but you would basically be looking at vacation rentals. You might have a hard time finding anything on the regular market. Even if you find something, it's not unusual for agent to ask for a fee (Provision) of up to two months rent when signing the contract, which would make the rent much higher if you only stay three months. On top of that, deposit can be up to three months' rent.
I think that intent is also important: If you are on vacation, even for three months, you don't need a permit or registration. If you want to work or make Germany your home, you would need to register and you can't do that with a visa from another country.