I assume that you are talking about the part in Chapter 11 where we find out what rewards are being offered for Pap (because people believe he killed Huck) and for Jim (because he has run away from slavery). The reward for Jim is $300 while the reward for Huck's dad is only $200.
The satire here, to me, is that the reward for Jim is higher. You would think the higher reward would be for the person who committed the more horrible crime. So Twain is satirizing a society where it is more of a crime to try to be free (if you are a slave) than it is to kill your own son.