At what point do you stop fixing a car: when the cost outweighs the value of the car or when you have lost your attachment (Sentiment) towards it?
If you enjoy your car, typically the average monthly expense exceeding the cost of a payment is a good time to stop repairing it. When you are shelling out, on average, $500-800 per month on repairs and upkeep, a new car of similar size and capabilities will be less in payments and come with warranties, free oil changes, etc. As part of the purchase. Not to mention so incentives that might apply if you are trading in a non-EV for an EV, or something else.