BGA vs SMD assembly costs
BGAs have superior reflow characteristics as they are pulled onto the pad during reflow (due to surface tension). Due to this effect, the placement accuracy for a BGA is slightly looser than for standard SMD components such as QFP and QFN.

QFP devices will solder wherever they have been placed.

BGAs are not a cure-all, of course; they have their challenges, particularly X-Ray post soldering, but I have had automated X-Ray testing on boards in the past that had a very low error rate.

QFP devices can catch the unwary if the PCB is tested by bed of nails or roving probe: I have seen devices where a pin was clearly not soldered, but the probe pushed it onto the pad, making an electrical contact during automated test only; the board failed a functional test, but as that is further down the process, it becomes more expensive to fix, under some circumstances.

In production, the cost of manufacturing is the cost of a pick and place which should be comparable for QFP and BGA devices on any modern system.