Its not just the ADC chip costs. At around $10 (approx) per ADC, it does not matter if i place 1 or even 10 ADCs - BUT there is also increased PCB space, size costs. Then also The routing and board layout costs.

I am not worried too much about the cost for this small quantity of boards i need at the moment, but keeping cost aside, what about the non-linearity and chip-to-chip-mismatch error ? If i remember correctly from what everyone has posted in here, the prime issue is to reduce the errors of multiple components in the system, whether that is the combined error of multiple IAs / Opamps OR the ADCs.

OR are the chips really manufactured in such a way that all such chips produced for a particular model would have exactly the same Drift, linearity and mismatch coeficients ?