Why did Yehudah agree to give a kid-goat, and the three objects as security? Why did Yehudah not simply pay her fee?
Oznayim la'Torah: Yaakov initiated a system of coins in Shechem, implying that other towns still employed the system of bartering goods. 1 Consequently, Yehudah offered Tamar a kid-goat, and three personal objects as security until it was available.
There were coins before this! Avimelech gave money when he returned Sarah. Avraham bought Sedeh Efron for coins accepted in all places (20:16, 23:16). Midrashim discuss how Sodomites would give marked coins to a poor man, and then take them back after he died; Lavan embraced Yaakov to feel for coins... (PF) Maharsha (to Shabbos 33b) explains that Yaakov minted coins with the image of the city on them.
Why did he say "Anochi"?
Ha'amek Davar: An Esnan is according to the honor of the Bo'el. A lowlier Bo'el must pay more. Yehudah said that for him, a kid suffices, and Tamar agreed.
