Midrasch zu Dewarim 24:2

And whence is it derived that she (a Jewess) is acquired (as a wife) by money? R. Yishmael says: It follows a fortiori, viz.: If a Canaanite maid-servant, who is not acquired (as a maid-servant) by cohabitation (with the master), is acquired by money, then a Jewess, who is acquired (as a wife) by cohabitation, how much more so is she acquired by money! And whence do we derive (the same for acquisition of a wife by) a writ? It is written (Devarim 24:2) "Then she may go (by a writ of divorce, from her husband's house) and become another man's wife." "Becoming" is being likened to "going" — Just as going is "going" is with a writ, so, "becoming." R. Akiva says: It is written (Exodus 21:10) "If another (wife) he take for himself (in addition to the maid-servant)" — Just as the first, (the maid-servant, is taken) with money, so, the second, (the wife, is taken) with money....

(Devarim 24:2) "And she shall go out of his house": We are hereby taught that the woman leaves the presence of the man (i.e., she leaves the house, not he.)