Or HaChaim on Exodus 35:27/אור החיים על שמות ל״ה:כ״ז

1 והנשיאים הביאו את אבני השהם, and the princes brought the onyx stones, etc. The reason that these precious stones are listed only after such relatively inexpensive contributions as the spun goats' hair by the women is, that the princes tarried and were the last ones to make their contributions.