I guess the main reason for your question is because you understand that wafer cost can vary based on different parameters, I will try to list them here:
– Firstly, the main price factor is related to the wafer technology node. Meant, that 65nm wafers will cost more than 180nm wafers.
– Then you need to consider the total number of mask layers. Meant, how many metal layers do you use in your design and whether you need additional layers for various options you might need: eFlash, MIM cap, HVT, LVT, etc all these features add more complexity to your wafer configuration and hence increase the price.
– Process maturity – of course the new processes will cost more money. A decade ago, I used 65nm process, the mask set price was 700K US$. This the price is half.
-Process defect density, when you buy wafers from any fab, you buy the good and bad wafers. Therefore, you have a big interest that the fab has high yield on the target process (ask them).
Hope it helps….