All of the insults during the final confrontation between Ron and Marcus were improvised on the spot as both Andre and Matthew playfully insult each other on a regular basis in real life.
The production cost was so low because all of the equipment was rented for free at the University of Missouri's library. The only thing actually paid for was the Brisk itself. Unless the tuition to school that allowed Andre to get these free rentals is in consideration, then the budget is much higher.