Unlike the half shekel that all males pay, these sin offerings have a paupers exception allowing the use of birds, or even grain. Lev. 5:7-13. (Reminds me of, "If you haven't got a penny, a half penny will do; if you haven't got a half penny then God bless you.")
Grain is definitely the lowest form of offering. This brings me back to:
Adam made love to his wife Eve, and she became pregnant and gave birth to Cain. She said, “With the help of the Lord I have brought forth a man.” 2 Later she gave birth to his brother Abel.
Now Abel kept flocks, and Cain worked the soil. 3 In the course of time Cain brought some of the fruits of the soil as an offering to the Lord. 4 And Abel also brought an offering—fat portions from some of the firstborn of his flock. The Lord looked with favor on Abel and his offering, 5 but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast.
6 Then the Lord said to Cain, “Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.”
Leviticus 6 & 7 are details about actually making the guilt offering, the burnt offering, the communion offering, the fellowship offering. I did not find much to move me in those bits.