I was just out for a quick walk and allowed myself some time to think about Apple's current pricing tiers.
Did a quick spreadsheet and found the following.
Apple prices Storage RAM at 78 cents per GB. It mainly holds true for all upgrades except on the 7/7plus where they rip you off a little (charging $100 for an upgrade worth $75).
Every processor generation bump is about $100.
A screen size bump is worth $100.
The change from LCD to OLED is $250.
Going from TouchID to FaceID (aka X-style) is $50.
NOTE - I had to consider the Xr as a small sized screen for this to work smoothly.
OK for those wanting a smaller X-style phone with an A11 chip, you can either build from an 8 or come down from an Xr.
Build up method
iPhone 8/64 - $600
TouchID to Face ID - $50
Total $650
Strip down method
iPhone Xr/64 - $750
Processor decrease - minus$100
Total $650
I guess if you want to consider the mythical SE-2 as an even smaller screen, take another $100 off and you end up at $550, so maybe it isn't too much of a stretch for Apple to price at $500 .. maybe put the base at 32GB.
With all that said, I doubt Apple would do this as it would eat into the sales of higher margin phones. Perhaps they'll throw a bone out there for the faithful.