But surely you can’t be suggesting that the homeless man should be housed for free, so that someone who has contributed so much to society has to bear the costs?

Maybe we should let the free markets decide: first, the criminal should sign a completely voluntary contract which specifies that his new owner is entitled to assign to him any work they deem a suitable compensation for his upkeep during his sentence (not signing the contract or shirking work duties leads to a doubling of the sentence and immediate transfer to an isolation cell for the remainder of his sentence), then put him up for auction and sell him to the highest bidder