How much did it cost, in dollars at the time, to develop the Zilog Z80 CPU?
According to Wikipedia,
The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples were delivered in March 1976, and it was officially introduced on the market in July 1976.
If this were a software product, with which I am more familiar, you could get a first approximation by taking the typical salary of a skilled employee, doubling it for total cost of employment, multiplying by twelve for the team size, and by ~18 months for the project duration. But I don't know whether a hardware product like a CPU and supporting chips, has other costs that are not small compared to the cost of employing the developers themselves.