They offered the 15" retina in 2012 for $2200. Before that, the 15" models with TN panels started at $1800-2000 with dedicated graphics. Apple basically charges whatever they feel like on the higher end models. I think it's somewhat decoupled from the cost of construction once you get away from the Their margins on those are probably much higher once you move past the 13" model or add cto upgrades.
Kind of, pricing seems to more closely follow Apple's consumer-facing logic, not the internal cost of development, bill of materials etc etc. So stuff like an upgrade from 256GB to 512GB costing $200 or 32GB RAM costing $400 over 16GB. I do think, though, the move to dedicated graphics only is why the 15/16" models since 2016 had such a significant base price jump.
The retina model settled back in at $1,999 starting price after 2012, when the Unibody was discontinued and an iGPU only retina model was introduced - though that did represent a permanent uplift of $200 as the Unibody had started at $1,799 as you mentioned. With the 2016 models, basically they only replaced the $2,499 (2015) model with dedicated graphics (giving it a $100 price cut but initially halving the storage to 256GB), while the $1,999 (2015) model was left on sale until 2018 but not replaced.
So now, with Apple Silicon, the opportunity is there to reintroduce that iGPU model/ $1,999 price point even if the model with the Apple GPU (Lifuka) continues like for like at $2,399. Whether or not they choose to do this I guess depends on whether the extra sales end up being worth it. A computer built around a SoC should be much simpler and cheaper to make than one with both an expensive Intel CPU and AMD GPU, even if it is a cutting edge SoC. I'm sure Apple won't sell themselves short, but if they target the 14" to take on the price of the current $1,799 (13") MacBook Pro, a scaled up 16" version at $1,999 seems quite a reasonable proposition.
