It (the car) cost $700, so the driver is unconcerned about damage as a result of an accident while merging. Lots of people on the road have this weird bully complex and actively prevent people from merging into their lane because they have faith that all the other drivers on the road care enough about their cars to not want to risk damaging them in a game of chicken. That really only applies to people who paid a lot of money for their cars and are hoping to retain some of that value for when they go to resell it.

Basically, the bumper sticker is warning people that if he starts to merge, he doesn't care if you speed up to close the gap in traffic, he's going to keep going and you'll probably the the one who loses money on the repair bill.