Be careful, an out of balanced rear wheel that has vibrations will eat up the electric motor's bearings. Reason I say this, I know a friend who's Roadster had a slightly bent rim that they kept driving on. Eventually the motor bearing failed and needed to be replaced by Tesla. I feel the vibration just rattles and shakes things in a way they become off-balance, and with bearings, balance is key for them to wear evenly with the least amount of stress.
Personally I wouldn't be driving on it. If it was a front rim, I'd wouldn't be ask picky but its the rear that's close to all the drivetrain.
I also feel it might be difficult to find a used rear wheel in the forged type since each rim is specific to the side as well as their diameter difference.
I'd seriously price a single rim from Tesla. Note they're much cheaper when buying all four, so you could put a feeler out to see if other's need the other 3 wheels and work out a deal.