The 6502 was already a much less expensive processor than its
competitors, because of a mask retouching technique MOS Technology
developed that saved mask iterations.
I saw that claim on Wikipedia. Is there any published reference?
There is book about the history of Commodore which is rather detailed
(and entertaining) about the MOS history, too:
http://www.commodorebook.com
The MOS chapter can be read freely here:
http://www.commodorebook.com/view.php?content=toc
Excerpt:
At MOS Technology, John Pavinen pioneered a new way to fabricate
microprocessors. "They were one of the first companies to use
non-contact mask liners," says Peddle. "At that time everybody was
using contact masks."
With non-contact masks, the metal die did not touch the wafer. Once the
engineers worked out all the flaws in the mask, it would last
indefinitely.
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I guess, Chuck Peddle is a good enough reference ;-)