If you cannot afford to do sacrifice, you need not worry. You incur no sin.  Allah does not place on anyone a burden if he or she has no strength to bear the same.

The Prophet (peace be upon him), said, “Whatever I prohibit you refrain from it; do whatever I bid you as best as you can. Previous nations perished because of their hair-splitting questions and straying away from the ways of their apostles.” (Muslim)

He further said, “If Allah is silent about something, deem it as being excused; for He has done it out of mercy for you, and not out of forgetfulness. Saying this, the Prophet, peace be upon him, recited the verse, “Your Lord is not forgetful.” (Al-Hakim)

While the Prophet told us to offer sacrifice, he said, ‘Those of you who wish to do sacrifice.” He did not say so definitely. The Prophet, peace be upon him, indeed offered sacrifice, and the companions also followed his example.

However, we learn that the Pious caliphs, Abu Bakr, and Umar, as well as companions like Ibn Abbas, did not offer sacrifice every year. Instead, they skipped it one year or two. When asked about it, their answer was lest people consider it mandatory to do so.

In conclusion, sacrifice for Eid Al-Adha is an excellent sunnah; however, it is not obligatory – even if one can afford to do so. So, there is nothing wrong if one were to skip it one year.

Allah Almighty knows best.