How to 'scientifically' calculate the cost of SEO?

Input1: Backlinks gap (difference of competitor backlinks to prospective clients backlinks)

Input2: Content gap (gap of clients articles on a topic vs competitors)

What other factors would you include to decide 'scientifically' on how much SEO should cost?

Note: The cost quoted to the client could be: Scientifically Calculated Cost + 50% margin = Client SEO Price

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