I'd go with a cost range of $70-86 Mn for a J-20, with a 70% confidence level.
The F-35A cost is $86 Mn (including engine) and has reached a floor.
My best guess is that the J-20 (including engine) costs $70-80 Mn.
However, there is a possibility that the J-20 is almost as expensive as an F-35A
And in another 4 years, the J-20 would drop another $10 Mn, as per the F-35 experience, because the Chinese are at an earlier stage of the production learning curve.
Methodology and all the assumptions below.
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We could use the F-35 as a reference, and specifically the Air Force airframe (excluding engines) as it is the most comparable to the J-20.
For 3 years from LRIP 5-7, the F-35 was at 35 per year. The cost dropped from $111 Mn to $98 Mn
Then it took another 4 years to ramp up to full rate production of 141 per year. The cost further dropped to about $80? Mn
After another 5 years to today, the cost has dropped to $70 Mn, and has reached a floor.
And the F-35 engine in 2023 costs another $16 Mn
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Back in 2018 (Chinese LRIP 3?), the J-20 cost was supposed to be $100-110 Mn.
And my guess is that we're near the end of the J-20 ramp to 100-120? per year.
If we go by the F-35 experience, that would imply the J-20 costs $70-80 Mn
So yes, the J-20 is a bigger aircraft with 2 engines rather than 1.
But there are lower overall costs in China, plus the Chinese are starting further behind, so there are more (and easier) opportunities to improve.
NB. This assumes engines are included in the J-20 costs.
But even if they aren't, the AL-31 (WS-10 equivalent) was $4Mn each back in 2013.
Even with inflation, you wouldn't expect 2 such engines to exceed the single F-35 engine cost of $16 Mn
The other caveat is that the final WS-15 engine still has to be put into mass production, and will presumably increase costs.
