My guess is this one will be similarly priced, because they use the same pass-through connection pins for the smart connector.
I think that part needs Apple’s license / API to build to make sure compatibility, hence they may need to pay for it and increase the production cost.
As for a bumper case, it needs to grip the edge a bit part from the front and back too, not just from the side.
So it will be impossible for the iPad to stick magnetically to the MKB because part of the bumper will be in between.
And the smart connectors won‘t be connected as well due to the gap.
Just my guessing.
In the meantime, my suggestion is just to use a skin like you said, maybe find a skin that covers the side part too.
It looks best without a case after all when using the iPad with the MKB.