Prison is not the right fit. If you want deterrence, make them pay directly towards the victims. Put them on house arrest. Put them on probation. Ban them from holding a managerial or executive role.
There are plenty of alternatives that don't involve locking people in cells - and that are probably more effective a deterrent.
While there are other options as you pointed out, I'm not sure it's realistic to say they're more likely an effective deterrent than prison.
People pay tons of money to avoid prison, even temporarily - see lawyers, bail, etc. Same goes for getting prison sentences reduced, even just in part, to house arrest and probation.
Just what amount of fines, house arrest, and probation is going to be more effective a deterrent than prison?
I think there's a reasonable discussion to be had about where the line is between 'enough' deterrence and excessive punishment, but it's a bit absurd to claim that things people happily accept in lieu of going to prison will be more of a deterrent than prison.
There are plenty of alternatives that don't involve locking people in cells - and that are probably more effective a deterrent.