The simplest and most expensive three phase charger imaginable would consist of three separate single-phase chargers, one for each phase. This requires zero engineering, but is enormously expensive compared to what's possible, because you throw away the three phase advantage of smoother rectifier output and need all components in triplicate. For comparison, the rectifier stage of a three phase charger is one and a half single phase rectifier, not three, and less than half as much total smoothing capacity is needed.
If the simplest solution is chosen, the cost would be three times the standard charger. If they build a real three phase charger (or source one), the cost might be something like 50% higher for the same amperage, but a good bit less per kW. A 32 A three phase charger would probably cost less than the standard charger.
For me, this is a question of wether I can buy it at all or not, so I'd be willing to pay more. The problem is that with the 300 mile battery, the car will be quite expensive already, and there is a limit to what I can pay.