These aren't useful numbers to compare. Even if the criminal gained zero material value from his crime (say he just enjoys setting cars on fire) the rest of society may be willing to spend a small fortune to stop him from doing so. Even a completely cold-blooded insurance company would be willing to spend money on that.
Dahmer, for example, killed because it gave him a sexual high and he didn't like having anal sex performed on him, so his gay boyfriends didn't work out and he sought to create a zombie who would never leave him via a crude lobotomy technique. I suppose there's some argument that even he reformed in prison--he converted to Christianity and later helped those studying serial killers--but I wonder how many people would have been willing to let him move in next door to test the extent of his reformation had he not died in prison?
None of this is to say that prison is good or even desirable. One of the worst things it has done is to create a culture for criminals and criminal gangs and thereby facilitate the growth of criminal organizations.
I don't have any grand solutions to any of this, unfortunately, but neither do I believe some of those offered by others.
About half of society strongly opposes letting criminals run free, out causing mayhem and destroying our civilization.
About half of society strongly opposes letting a judge order a bailiff to fix the issue with a $0.25 bullet as soon as the verdict is in.
That leaves us with the option nobody likes, which is that we spend an absurd amount of money keeping people incarcerated. Most of society grudgingly accepts this.
I have. I escaped without losing anything - I can cross "jumped out of a moving cab at gunpoint in Panama City traffic" off my bucket list - but it left an emotional scar. Nothing lifechanging, but there's a little bit of anger that wasn't there before.
I'd love to explore evidence-based alternatives to incarceration. I'd also consider caning - but only if it really hurt.
That's incalculable. You can't reduce the effects of crime to basic capitalist mechanics. Crime doesn't only impact the fair market economy - there's a wealth of second order effects both on people and at a macro level.
You're right that there's other levers we can use to reduce crime that don't involve simply bolting a door shut on them, but it seems an odd way to argue the point to me.
If I told my right wing, tough-on-crime uncle that keeping people in prison was expensive, he'd say we should just shoot them as bullets are cheap, or possibly that we should cut 'luxuries' like gym equipment and free education, charge prisoners rent and force them to do hard labour.
I think people who would advocate for a more Scandinavian system are unlikely to convince my uncle on cost grounds.
Bullets don't need to be cheap. China solved the cost issue: simply charge the family for the cost of the bullet.