Doing it properly will indeed allow you to launder hundreds or millions, but the more money you try to launder like this the harder it is to actually do it without being noticed. If you have a small business that accepts cash payment you can easily pad your income with anonymous drug cash and nobody will be the wiser, but if you run a small business and make ten million dollars over night in cash people are probably not going to believe you . When it comes to big money you need to have front companies and fake identities in other countries and bank accounts and all kinds of shit that I don't really know much about. But if you are working with tens of thousands of dollars extra a year it is a lot less complicated to launder it while staying under the radar and looking legitimate.