Which lower price models? iPhone 7 and 8?
The lower price models are all old designs from 2017 and before. The 2018 iPhone models are all newer thin-bezel with Face ID. From a consumer's view, 3D Touch is nice to have, but the 6.1" model wins hearts and minds due to the form factor, Face ID, and A12. Software simulated 3D Touch is probably good enough for most users.
Think of the iPad (2018). Unlike the iPad mini 4 or iPad Pro, it doesn't have a laminated display. But the 9.7" display combined with A10 and Pencil support wins over consumers.
Yeap, you could have the 7 Plus and 8 Plus with 3D Touch cheaper than the new cheap 6” device with X bezelless design. Which will be odd.