The best punishment for financial crimes is financial punishment. That means stripping them off their wealth forever until they can pay back what they stole plus fine and as an added bonus community work on weekends. It's a lot healthier than prison and it's beneficial for everyone.
Prison should be to protect people on the outside from violent people not as an extended slap on the wrist. A violent person goes there to cool off, so that he may become non-violent once he is released. There is really no point in putting non-violent people there. At some point the harshness of the punishment becomes irrelevant and there is no difference between doing community work for life or rotting in prison.
In my opinion punishment should focus more on the improvement of the individual and society rather than just be pure punishment with no benefit whatsoever.
There are several flaws in that logic though.
You assume that people who commit financial crimes to be wealthy. So what's with a poor guy who is in serious debt and yet keeps buying TVs, mobile phones etc. with money he doesn't have? Do you think he cares that he gets a financial punishment? You can't stop his future actions that way.
So the alternative would be community work. And how exactly would you enforce that? A fine wouldn't help at all as stated above so the only chance would be to threaten him with a prison sentence.