What is "Motza ha'Susim"?
Rashi: It is the source (it was from Egypt).
Radak citing his father: One may take horses out of Egypt only with the king's permission; one pays to do so. Pharaoh gave it to Shlomo 1 ; Shlomo sold it to merchants for a year, for a known price. They would buy from the king Mikve ha'Motza, i.e. the collection of the entire export. [Shlomo's merchants] were in Egypt and received the price (tax) for taking out horses.
Kli Yakar: He did so because Shlomo married his daughter. Shlomo received great wealth from this!
What is "Mikve [Socharei ha'Melech]"?
Rashi: It is the gathering [of horse merchants in Egypt].
Radak: Mikve is like "Tikvas Chut ha'Shani" (Yehoshua 2:18). Shlomo got horses and linen threads from Egypt. [Also] linen of Egypt is high quality - "Shesh b'Rikmah mi'Egypt" (Yechezkel 27:7), "Chatuvos Etun Egypt" (Mishlei 7:16).
Malbim: It is where they raise horses. Many horses are gathered there.
Why does it say "bi'Mchir"?
Radak: Shlomo's merchants bought horses [and linen - refer to 10:28:2:2] from Egypt for the price (exchange for) other matters that they brought from Yerushalayim to Egypt.
Malbim: Shlomo's merchants bought the entire collection of horses raised, so they could charge whatever price they wanted to.
