He says that even Yosef's undercoat was hurriedly removed in their great anger. The Kol Bo on Chanukah goes further. They both say that the brothers DID NOT SELL Yosef. There are numerous opinions as to the amount given for the sale of Yosef. Possibly, there might be another correlation.
Shoes are the base upon which a person stands.
Similarly, the half-shekel was used for the silver foundation blocks which held up the Mishkon beams. The sale of the Tzadik Yosef was for money. The Moshav Z'keinim asks from the gemara Gittin 57b that relates that the blood of the murdered kohein Zecharia was compared to the bloods of different sacrifices including that of goats, and did not match. Had he stood strong, his brothers would have been persuaded to change their position. We see from here that a true leader cannot be swayed by public opinion, even when he is but a single voice.