Earlier quoted context omitted.
It's a pretty accurate cost estimate from those tracking Ax series costs. A chip AMD sells for $300 doesn't cost AMD $300 to make, but being a public company their gross margins tell us it costs roughly $150.
But you were comparing this theoretical production cost to the retail cost of other chips, that doesn't make sense. Hardware companies don't charge cost + some reasonable markup, they charge whatever the market is willing to pay for it. I highly doubt Apple would release some hypothetical "threadripper killer" at a price any lower than they needed to to compete.
Lets assume that all the other parts, high speed RAM, SSD, power supplies, cooling, motherboard, etc cost another $500, and that operations, assembly, marketing etc average 20% and the manufacturer aims for a 5% margin. So they sell their low end Threadripper PC for $3300, and their high end Threadripper for $4,700.
Then Apple comes along and makes it's own high core count versions of the M1 (lets call them the M16 and M24) for $1,000 and $1,500 with similar performance to the Threadrippers. When Apple builds high end Mac Pros out of the, they also spend $500 for other parts, giving total parts cost of $1,500 and $2,000, it marks them up 50% for their typical margins, and sell them for $3,000 and $4,000 and have the same performance as the ThreadRippers from the lowest margin manufacturers at for 10-15% less.
And on top of that, the M16 and M24 use less power and generate quite a bit less heat than the Threadrippers. They don't need any fancy cooling systems. That can lead to smaller packaging and even more cost savings.
Obviously when Apples 16 and 24 Firestorm core Mx chips come out newer Threadrippers will have evolved to smaller process as well, and that will help increase their performance, while reducing cost and heat. But there is little doubt that Apple's Mac Pros will be much more competitive price and performance-wise at that time, and if they keep leveraging TSMC first there is a significant risk that they actually take some of their laptop cost/performance advantage up to Threadripper levels.