Well, yes. Technically $450/ea. The only other option is Planted Technologies which are $199 just for the mount. You can live with the stationary seatbelt mount but we definitely do not like that. We opted for a boxed/welded bracket that won't move under sever use especially off-road. We also wanted to take advantage of the space but adding storage to the setup. Simply not possible with the other option.
Also keep in mind that regardless of your seat mount choice you still have to add $150 to the cost of sliders per side.
Absolutely. But you don't get a seatbelt mount that moves with the seat, you don't get a rigid seat mount that won't move no matter what the situation, and you won't have access to storage under the seat.