וַֽ֠תַּעֲלֶה וַתֵּצֵ֨א מֶרְכָּבָ֤ה מִמִּצְרַ֙יִם֙ בְּשֵׁ֣שׁ מֵא֣וֹת כֶּ֔סֶף וְס֖וּס בַּחֲמִשִּׁ֣ים וּמֵאָ֑ה וְ֠כֵן לְכָל־מַלְכֵ֧י הַחִתִּ֛ים וּלְמַלְכֵ֥י אֲרָ֖ם בְּיָדָ֥ם יֹצִֽאוּ׃ (פ)
애굽에서 내어 올린 병거는 하나에 은 육백 세겔이요 말은 일백오십 세겔이라 이와 같이 헷 사람의 모든 왕과 아람 왕들을 위하여도 그 손으로 내어왔더라
Ibn Ezra
enthrone your brother if he be not an Israelite (e.g., an Edomite, even though he is called “your brother” [23: 8]). The reason for the law about the horses is that in those times horses were imported from Egypt. The evidence is the passage “a chariot going out of Egypt…” [I Kings 10: 29], which occurred during Solomonic times. Because of Solomon’s need for their horses, he caused the people to sin and to return to Egypt. Obviously, it is a disgrace to return to Egypt after God has redeemed us from there (Uriah the prophet fled there only because his life was in danger [Jeremiah 26: 21]; and Jeremiah went there against his will [Jeremiah 43: 5-7]).
Rashi
לא ירבה לו סוסים HE SHALL NOT MULTIPLY HORSES TO HIMSELF — but he shall have only what is sufficient for his carriages, in order that he shall not cause the people to return to Egypt, because horses come from there, as it is said in the history of Solomon (1 Kings 10:29) “And a chariot came up and went out of Egypt for six hundred shekels of silver and a horse for a hundred and fifty” (Sanhedrin 21b).
Rabbeinu Bahya
רק לא ירבה לו סוסים, “only he shall not amass for himself horses, etc.” The Torah now proceeds to list differences between Gentile kings’ prerogatives and those of a Jewish king. Jewish kings must not make the acquisition of many horses and chariots their policy. Neither must a Jewish king amass gold and silver or even wives. Gentile kings see in the acquisition of these possessions an end in itself and treat these possessions as the measure of their success instead of as something secondary as Jewish kings are asked to do. A Jewish king is to make preoccupation with the Torah his principal concern. This is why the Torah not only demands that he write (2) Torah scrolls but also that he read in it daily; this will teach him reverence for the Lord (verse 19) and will ensure that he remains on the throne for many years.
Sanhedrin 21 interprets the words “that he do not amass many horses” to mean that he should not amass more horses than he needs for transportation for himself and his soldiers. He should not have a selection of chariots at his disposal to ride in and alternate between them. The reason for these restrictions is spelled out, i.e. not to bring the people back to Egypt, the country from which horses were exported in those days. We read in Kings I 10,29 that the cost of a chariot imported from Egypt in those days was 600 silver shekels whereas the price of a horse was 150 shekels.
Sanhedrin 21 interprets the words “that he do not amass many horses” to mean that he should not amass more horses than he needs for transportation for himself and his soldiers. He should not have a selection of chariots at his disposal to ride in and alternate between them. The reason for these restrictions is spelled out, i.e. not to bring the people back to Egypt, the country from which horses were exported in those days. We read in Kings I 10,29 that the cost of a chariot imported from Egypt in those days was 600 silver shekels whereas the price of a horse was 150 shekels.