Yeah, I also have read/seen the "Cargo Kit" option & was mention in a video by slate member who said he built his with the suv cap with no rear seats to have space for his dogs.
I believe the suv kits include everything (top, roll bars w/airbags, rear seats, & installation accessories). I feel on the high side, but you know.
I hope they provide optional kits. I do not want rear seats at all, therefore no need for roll bars & airbags. I just want the suv top. If that...