I still don't accept the buy-out in principle.

1. I don't think you can accomplish both deterrence and equal justice with any possible implementation of your idea. For deterrence to be accomplished, we have to consider the fact that most crime is committed by poor people. What good does it do to allow a robber to buy his way out of a sentence if he will steal (or has stolen) the money he'll use to pay off his sentence?

2. Prison is preferable to buy-out in part because it is horrible. A buy-out puts a crime on the same moral footing as a financial transaction. I can buy a house, I can buy the right to rape a 13-year-old girl. Prison puts the transaction on an a morally equivalent level--you have done something outrageous to society, we're doing something outrageous to you. You raped someone; she had no choice. We're now taking your choices away from you.

3. Even on a practical level, you option may not protect society as well against repeat offenders. Bill Gates pays 95% of his net worth to commit rape. Now he's free, he can commit another rape. He has less money now, so the second rape cost him less than the first.

4. Prison may help deter the rational, plus it incapacitates the irrational.