$32 Billion dollars to be exact. 
https://www.unodc.org/documents/human-trafficking/UNVTF_fs_HT_EN.pdf

Sure. A few thoughts.

1.  The people behind sex slavery numbers have been known to sensationalize things by including all kinds of voluntary sex workers as 'trafficked sex slaves', so I would look at these numbers very, very skeptically.
2.  If this is a big problem now, it is a failure of whatever protection services exist in the moment  (i.e. governments)
3.  By making prostitution illegal, the trafficked workers are treated as criminals instead of victims.  So really this is another prohibition problem that wouldn't exist.
4.  Even if it is 32 bil industry (I still think a lot of that is just consensual sex work ), its not a single 32 billion dollar organization to try and fight.  There are a lot of much smaller operations going on.  And that number might be impressive until you look at what the insurance industry is worth.
5.  No one is going to pay for kidnapping insurance that doesn't include attempted recovery services.  No one would just accept a payout and not try to get the loved one back.
6.  Security personnel would be all over this.  You know all those cop movies and dramas where they get pissed off doing bullshit and they can't fight real crime?  This would be the most glorious and satisfying work a security firm could be engaged in.  Employees would be chomping at the bit to get assigned to these cases.