I think you can loss money in the current game without negative profit slider...
If your cost (tooling cost + engineering cost + [cost per car x cast per day x days of production]) is lower than (price per car x cars sold) [asuming you sold al your cars] then you would be losing money.
Example:
Asuming 200 days of production and a market price of 39,396 (8%) and following the formulae above, the total production car would be $1''403'143,800, and the total amount of sales would be 1''011'808,800. And that's assuming that you sold every car you produced (which is kind of unlikely). Of course you can produce more and more cars until you get back what you invested, but thats the case for production cars. But in the case of hypercars or vehicules that are limited production, you can easily loss a lot the money.
This is another example. If we set this car to be limited to 300 cars, with a market price of $87,472 (12%), after doing the calcs we get that the total cost of making the 300 cars is $574'237,800, but we only get back $3'761,296.