Historical price charts for RAM are quite readily available, e.g. in the mid-seventies a ballpark figure was a penny a byte. What was the price of ROM (assuming you were getting the chips produced in quantities at least a few thousand) in that time period? I imagine it was cheaper than RAM, but by how much? (Every Google search hit I find, assumes I'm misusing ROM to mean anything from flash memory to magnetic tapes, which is a weirdly rapid timescale for a term to decay.)
We can infer the price of one of the first ROM reading the agreement signed between the Japanese Nippon Calculating Machine (later Busicom) and Intel in February 1970 (available here). The agreement provided for manufacturing of a set of 4 chips: RAM, ROM, shift register, CPU (this was the famous Intel 4004, made by Federico Faggin). ROMs cost consisted of a fixed part and a variable part. Fixed part was:
- $60k as development charge of the 4 chips. The breakdown of this cost is: about $15k for RAM, $10k for ROM, $5k for shift register, $30k for CPU
- $2k ‘as the tooling charge for each ROM separately’. NCM undertook to purchase 60k kits of the chips with the cost dropping with volume: The first 50,000 ROMs cost $13 each with each additional ROM costing $12. The cost per bit can be found recalling that the ROM stored 256 8-bit words, i.e. 2048 bits.
You can get a sampling of prices for EPROMs the hard way, by checking ads from electronics magazine archives. For example on page 116 of Popular Electronics Jan. 1977 you can see the 1702A 2K(bit) EPROM listed for $12.95. The old magazines always had full-page ads with components near the end.