Tzaddikim said that if people knew the value of the esrog, they would spend all the money in the world to acquire one.
The Gemara (Succah 41) tells us that Raban Gamliel once paid one thousand zuz for an esrog. "This teaches us how much they loved the mitzvos."
Until not very long ago, esrogim in Eastern Europe were extremely expensive because they had to be imported from Italy or other countries. In those days, there were only one or two esrogim per community, and they were costly. Therefore, for months in advance, the Jewish community would save up money for this purchase, and they did it with joy, wanting to keep this precious mitzvah.
One year, there were very few esrogim available on the market, so the Vilna Gaon zt'l gave a couple of his students a large sum of money and instructed them to seek an esrog. The students searched hard but couldn’t find anything. Finally, they found someone who had an esrog. However, this man wasn't an esrog merchant; he wanted the esrog for himself. The students offered him a lot of money, but he refused to part from his precious esrog. They explained that they needed it for the Vilna Gaon. Finally, he agreed to sell it on condition that he would get the reward of the Vilna Gaon’s mitzvah. The students feared that the Gaon wouldn't be happy with this condition, but having no choice, they agreed. The Vilna Gaon was extremely pleased when he heard about the condition. He explained that this was his opportunity to perform the mitzvah entirely lishmah. He won't be getting Olam HaBa for the mitzvah, so his intention will be solely to make a nachas ruach for Hashem.
Reb Yonason Eibshitz's zt'l would spend a lot of money to purchase a beautiful esrog. His student, Reb Hirsch of Hessin zt'l, would testify that Reb Yonason Eibshitz zt'l would buy an esrog, and if he found a more beautiful one, he would buy that one. And then, if he found an even more beautiful esrog, he would buy that one, too. His succah was also decorated with costly items. His students write, "All his money was valueless to him when it came to loving Hashem and His mitzvos."
There are different versions of the following story, and I will write it as I received it: Rebbe Michel of Zlotchov zt'l was very poor; sometimes, his children went hungry. But there was one item of value in their home. It was an inheritance of the holy tefillin of Reb Michel Zlotchover's father, Reb Yitzchak of Derohovitz zt'l. Reb Michel refused to sell them. His Rebbetzin zt'l often pleaded with him to sell the tefillin to support their family, but Reb Michel refused. Once, a wealthy person came to Zlotchov and offered a lot of money for the tefillin, but Rebbe Michel turned down the offer. "My father's tefillin aren't for sale," he explained simply. But there was one year when there were hardly any esrogim in Eastern Europe. One esrog merchant came to Zlotchov with an esrog, asking for a lot of money. Reb Michel sold the tefillin and bought the esrog for fifty reinish. Rebbe Michel's joy was endless. He had a beautiful esrog for yom tov. His surprised Rebbetzin asked him how he had money to buy the esrog, but Reb Michel didn't respond. She asked again until he told her that he had sold the tefillin. She angrily said, "I asked you to sell the esrog for our family, but you refused, and now you sold it?!" And with that, she bit into the esrog. Rebbe Michel said, “Ribono Shel Olam! I don't have the tefillin anymore, and I don't have an esrog either. Should I also be angry?!" That night, he saw his father in his dream. His father told him that he performed a great deed when he sold the tefillin to buy the esrog, but the second deed, that he controlled his anger, was an even greater accomplishment. His father said, "Your ability to control your anger was more precious in heaven than your mesirus nefesh to buy the esrog. Many gezeiros raos [harsh decrees] were annulled in the merit of your restraint."
