Italy and Spain have even smaller defence budgets than Britain. If you put the loss of 60 potential buys against their combined 80, it could well push the price over the threshold which they are prepared to consider.
I can't comment on how the USMC would cope with the price increase if their 400+ airframes were no longer discounted by a foreign sale of 140.
It would be ironic indeed if the F-35, an aircraft designed from scratch around a STOVL lift system, was only ever produced in a CTOL configuration!