This is half the price of a slave (Exodus 21:32), an indication of the depth to which Gomer had sunk in her harlotry.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8