Am I obligated to fulfill the vow of sacrifice that I made upon recovery, given the difference in my estimation of the cost of the sacrificial animal? And is it permissible for me to donate its value or sacrifice in partnership? And is it permissible to delay the fulfillment of the vow?

The vow must be fulfilled when its condition is met, which in this case is healing. It is permissible to fulfill a vow sooner than its due time if it is of the nature of charitable donations. It is not permissible to substitute the sacrifice with its monetary value or to share in it, unless the assistance from others is in the form of a gift. It is permissible to delay the sacrifice if one is unable to perform it.