I can't say the pricing looks right or makes sense at face value either. However, looking closer the 12x135 and 12x142 hubs are at least somewhat different in design than the 135QR hub.
The hub shell is different, with the right side flaring out much larger than the 135QR version, which means the engagement mechanism must be larger and/or different in design. My 135QR version only has 12pts of engagement, so maybe (just throwing this out there with no proof, just random speculation) the thru-axle versions could have something better?
The axle ends on the 135QR version have locknuts with wrench flats tightened up against the bearing covers, which are all threaded onto the axle. The 12mm versions appear to have a completely different design with no wrench flats, so there are probably more differences beneath the surface in the design there too.
The SRAM Spare Parts diagram confirms that the 12x135/142 versions use not only a different axle and hub bearings but a different freehub body than the 135QR as well. Unfortunately it only shows an exploded diagram for the 135QR version
Given these possible differences, it seems strange that the 12mm and QR hubs even share the same X.9 name at all. Even more so when there is apparently no design difference between the X.7 135QR and the X.9 135QR, just a sticker and supposedly a slight weight difference