Add up your individual cost of;
Accommodation
Utilities
Education
ALT's
Medical & Dental (commensurate reduction in medical staff requirements and insurance costs)
Visa
Percentage of savings due to staff retention prior to retirement age
Percentage of training costs saved as quality of applicants improve
...anything else (?)
less
tax in your domicile or whatever is required to make the salary adequate.
equals
Savings/Cost of basings.