Oh wait, that's wrong - he actually paid 200. From Sparklesdelicious
2 Samuel, Chapter 3 - This chapter is basically about the civil war between the up and coming House of David, and the ever-weakening House of Saul. David has about seven wives by now, and is pumping out children like no other. This news of giving birth to more children was probably great news in the Bronze Age; nowadays people wouldn't be nearly as excited. In any case, I think the news of all these children is a sign that the House of David is gaining power, and is in favor with the big guy upstairs, also know as God or Yahweh.
Finally, Abner (the last of the House of David) asked for a truce between he and David. David agrees, but with a very odd term. Abner may not see David's face until he brings Michal, the daughter of Saul. Michal was David's previous wife, whom he had actually bought for 200 Philistine foreskins (although it says 100 in this particular section), and then later "gave" her to a gentleman named Phaltiel. So, Abner fetched Michal to give to David, and her husband Phaltiel followed behind crying. That's just messed up.
Later, Abner is assassinated by the brother of Asahel, whom Abner had killed in the preceding chapter. King David was pissed at this, and basically cursed the assassins for their deed. He cursed them and all their descendants to a life of being poor lepers.