The attack is directly on the notion of lying itself (not necessarily having anything to do with money).
The point is that it controverts the use of language, which is something necessary to us. If everyone lies as much as they want, and does not feel bad about it at all, then we will be confused all the time as to what they do or do not actually believe. No one would harbor the expectation that statements were trustworthy. And therefore any given lie would no longer deceive. So the idea of lying would no longer mean anything. That is a contradiction in concept -- too much lying removes the possibility of the effectiveness of lying. And in so doing it removes the ability to communicate directly at all, which would be a major loss.
There is no disputing the logic there. The question is not whether the things he has defined exist. The question is whether their existence actually matters. That, he 'proves' by taking up 'autonomy' as his principal value, and applying a very simple version of the Golden Rule in a ruthlessly rigorous fashion. If you were the extortionist, you would not want everyone to lie to you. We need to more directly address the morality of extortion, rather than working around it by thwarting its effects.
Otherwise, we are not addressing morality as a community, we are using the criminal to justify our own misbehavior. Once you do that with one category of misbehavior, it applies to a wide range of things you might forgive, including extortion of your own. That is using a human being as a mere means to our own psychological comfort.
So he has foreseen your argument, and he addressed it explicitly, even down to the idea that you should not lie to prevent a murder.
That does not prove he is right, but it does mean that you need to make that more global decision for some other reason.
OK. A perfect duty has to come from a contradiction in concept. And, at least for Kant, a perfect duty, if it can be determined always overrides a contigent duty -- one where the maxim allows for conditions or measures.
The duty against murder is perfect -- if everyone killed someone, there would be no one left to kill.
The duty against lying is perfect -- if everyone lied all the time, no one could lie effectively.
The duties you put forward, like preventing criminal activity or managing the population size, are duties, but they are contingent, because autonomy allows different notions of criminality or deprivation, in a way that death or the ability to communicate do not involve different versions and degrees.
You can punish criminals, or not, and still be able to punish criminals, or not. There is not a level of letting crime be profitable where it is no longer possible for crime to be profitable. (Quite the opposite.)
You can breed, or not, and still be able to breed, or not. Having another baby in a world at peak capacity remains possible -- that baby would just be incredibly unfortunate.
In an asymptotic sort of way, badly handled contingent duties allow things to go badly wrong, but there is not a point where neglecting the duty makes continued neglect of the duty absolutely logically meaningless.
Badly handled perfect duties make for a conceptually contradictory world.
For Kant, the perfect duty always supercedes the contingent duty, because of the way the metaphysics that underlies the ethics works. You don't have to agree with that metaphysics. But there is not a conflict here that Kant has overlooked.
There is a rule in Kantianism for exactly what you are complaining about in this case. You can ignore the distinction that matters over and over again, but that will not change the fact that this is addressed in Kant's writings.
Klocking already pointed you at the sources in comments, so I am not going to redundantly do so again.