Is it permissible to pay a monetary fidyah in lieu of fasting the days one has vowed, and what is its amount?

If the vow is to fast or perform an act of obedience, it is obligatory to fulfill it. If a temporary excuse arises that prevents its fulfillment and is expected to cease, then one waits for the excuse to be removed and then fulfills the vow. However, if the excuse is permanent, then the obligation is to offer expiation for an oath (kaffarat yamin) for each vow, which is: feeding ten poor people, or clothing them, or freeing a slave. If none of these is possible, then fasting for three consecutive or non-consecutive days.