Setting up a discount paradigm that goes from slowly discounts vehicles from 100K all the way down to 15K after 8 hours plus a nice bridge loan to eat the losses and voila.
Marketing $15K as luxury vehicles sounds like real world activity to me, but… I think it might be a bug. 
Ha. well done. I guess technically you did beat the challenge…but at what cost to future profits???
It just sort of happened as a result of steep discounts over time. I did do it without discounts too… that took a little longer.
I find this game fascinating. Not least of which being the ease to make money. The only way to jeopardize profits is … to make more cars. It is my biggest concern that once i run out of the artificial challenges driving me to up production, the challenge would go. But at 162 real hours, still haven’t got there.
I keep coming back to random maps/challenges and score ladders as the perpetual challenge, or maybe even multiplayer for Production line 2… but for now, i just keep trying to build more cars despite the risk because … its fun