What moves the price
Days, first and always. Two days a month of genuine board-level attention is a different product from eight, and it should cost less than half as much. Be suspicious of a flat fee that never states the days behind it.
Delivery, second. Leadership-only pricing looks cheaper until you add the freelancers, the agencies and your own evenings needed to ship the plan. When you compare quotes, compare the cost of the outcome, and read the small print on who actually does the work.
Specialism, third. An operator who knows your sector prices with confidence because they are not learning it on your retainer. Generalists discount; the discount is your risk. A fractional CMO who has run marketing for recruitment firms before knows what a mandate is worth and where they come from.
The thing that should not move the price is theatre: office days for their own sake, decks nobody asked for, a weekly meeting that could have been a Loom. You are buying decisions and outcomes, and the invoice should read that way.