Is it permissible to give the price of the cow and distribute it instead of buying a cow after vowing to buy a cow and distribute it?

If what you said was with the intention of making a vow (nadhr), then it is a vow that must be fulfilled. If you did not intend to make a vow, then it is not considered a vow, but it is preferable to fulfill it. The principle is that whoever vows an act of piety must fulfill what they vowed, and it is not permissible to change it to something else or its monetary value. This is the view of the majority of scholars. As for substituting with money due to need and for the benefit of the poor, there is a difference of opinion, but it is permissible. However, substituting with money instead of slaughtering to alleviate the difficulty of distribution and similar issues is not permissible, unless it is for the benefit of the poor. It is always preferable to offer what was vowed in its original form to avoid disagreement.