Is it permissible for a Muslim who is able to perform the obligatory Hajj to delay it so that his parents may perform Hajj using his money?

If the parents are able to perform Hajj with their own money, then Hajj is obligatory for them. If they are not able, and you have enough money for your Hajj and theirs, then it is more appropriate that you perform Hajj with them. However, if your money is only sufficient for you, or for them, then start with yourself; because Hajj is obligatory for the able person immediately, and they are not obligated to it due to lack of ability, in accordance with the Almighty's saying: "And [due] to Allah from the people is a pilgrimage to the House - for whoever is able to find thereto a way."