Why did the kidnappers want 105 grand? (spoilers)

Warning: spoilers

Seems an odd number. Why 105, and not 100 grand even? I found the premise a little far fetched, implausible, but possible. He should have known that there was no way they could keep a dead body intact, however, a dead body isn't needed to tie someone to a murder anyway. I was constantly amazed at how calm and cool he was throughout the movie. He seemed to show little emotion... perhaps this was just the kind of guy he was, but it made it a little unrealistic. I mean, these guys could have come and killed him or his wife at *any* time. He had no idea what they were capable of. He was overly confident. The girl's death was actually partly his fault. If he had paid them instead of sending them that note, she'd have been alive. Of course, he had no way of knowing that. If it were me, I think the best option would be to simply leave the country.