Is buying the sacrificial animal considered disobedience to one's father if he forbade you from it after you saved up its price from your own personal allowance?

The Udhiyah (sacrifice) is a recommended Sunnah and not obligatory according to the majority of scholars. Obeying parents in matters that do not involve disobedience to Allah is obligatory. A recommended act should not be given precedence over an obligatory one. However, if a father prevents his son from a recommended act without a valid reason for the prevention, then there is no sin upon the son for disobeying him.

Therefore, obey your father in not purchasing the Udhiyah if he has a valid reason for the prevention, such as knowing your financial hardship. If he does not have a valid reason, then his obedience is not binding upon you, especially if you believe it to be obligatory and are able to afford its price. However, we do not think you are capable as long as you receive your allowance from your father. Your father's Udhiyah suffices for his household, and you are included among them as long as you are not financially independent.