Charles Ellicott Commentary Leviticus 14:21

"And if he be poor, and cannot get so much, then he shall take one he-lamb for a trespass-offering to be waved, to make atonement for him, and one tenth part [of an ephah] of fine flour mingled with oil for a meal-offering, and a log of oil;" — Leviticus 14:21 (ASV)

And if he is poor. —The benign consideration for the poor which has been demonstrated on previous occasions in connection with the sacrifices (Leviticus 5:11; Leviticus 12:18) is also shown here. Three lambs and three tenth-parts of flour were more than a poor leper could afford to bring. In such cases, therefore, all that was required was one lamb, which constituted the trespass offering, and one tenth-part of flour for a meat offering, and the log of oil which was needed for his consecration.