In order for it to be obligatory or Sunnah to offer the Qurbani, it is stipulated that the one who offers it should be independent of means, in that the price of the Qurbaniis surplus to his needs and the needs of those on whom he spends. If a Muslim has a salary that comes to him every month, and this salary is sufficient for him and he has surplus money which which he can afford the price of the Qurbani, then in his case it is prescribed for him to offer the Qurbani.
The fact that it is stipulated that he should be independent of means is indicated by the words of the Prophet Muhammad (ﷺ) : “Whoever can afford it but does not offer a sacrifice, let him not come near our prayer-place.” Narrated by Ibn Maajah, 3123; classed as Hasan by al-Albaani in Saheeh Ibn Maajah. What is meant by being able to afford it is being independent of means.