Neither Tesla nor most other front line dealerships will want your beater. They only accept it as a trade in, so they can sell you a brand new car. They will immediately dump it into an auction. They have cost to doing this, and risks to take, so don't expect a huge windfall. Tesla has no facilities to rehab old trade ins for resale.
Like all car deals, you need to shop your car around, to see what the current market is for such a vehicle. See who wants it the most and sell it to them. No need to bundle your sale of your old car with the purchase of a new one.
GLWS.