Investigative journalism costs a lot of money. Media houses therefore often face huge challenges, when trying to figure out how to finance investigative journalism.
There are media houses that finance investigative journalism using their advertising revenues. They do so knowing that investigative journalism reports are likely to draw huge audiences, which are in turn likely to translate into even higher advertising revenues. Thus, in these media houses, the justification for investigative journalism expenses (which are often huge) is in the argument that the investigative journalism reports are likely to bring huge audiences — which would in turn translate into huge advertising revenues. Under this model, the huge expenditure of money on investigative journalism is seen as an investment.
There are other media houses that depend on money from various government and non governmental agencies to finance investigative journalism. The said governmental and non governmental agencies are typically keen on propagating certain agendas. Some of the governmental and non governmental agencies in question pay for the investigative journalism reports directly, but most of them prefer to do so indirectly: through proxies and in other clandestine ways.
At yet another level, there are media houses that operate a system where people who wish to have investigative reports carried pay for the same. Thus, for instance, if you wish to have the corrupt dealings at a certain organization exposed, you pay a media house (through certain agents) to carry an investigative report on the same. There are people who will argue that this arrangement is not entirely ethical. But if, as a society, we are willing to accept the concept of privately run jails, and if we are willing to accept the concept of sending people who can’t pay debts to civil jail, then there is really no reason as to why we would have qualms about the idea of people paying directly for investigative journalism reports to be run. Admittedly, the whole thing does get murky when you have people paying for (potentially damaging) investigative journalism exposes to be run against their business rivals. But then someone will argue that trade is war, and that ‘all is fair in war and in love’.