Value-based pricing strategies

How does one use value-based pricing strategies in their fixed-fee
projects? Do you employ some sort of formula to derive the value price
based on your client's projected ROI for the project?

Specifically, if I target the healthcare vertical, do they expect a
customary ROI within a given timeframe? i.e. 100% ROI in 24 months, or
150% ROI in 36 months, etc? Hypothetically, if I get a conceptual sale
of a system that can reduce their costs (or increase reimbursements)
by $1M/year, is the value-based price I quote in my proposal to be
some function of that $1M and time? Is $300,000 (or more) for 9 months
of my time to get them to realize that $2M ROI in 24 months reasonable
and attainable?

Thanks so much!

Regards,
Mark A. Richman