Usually a few million dollars are enough. Maybe even less. Pumped coins always have low volume and therefore can easily get manipulated.
I think that they need way less money for their pumps. Its usually low cap coins which are getting pumped, some of them dont even have a daily volume of 10k.
Nevertheless please stay away from such groups as far as you can. The SEC is already hunting down such groups and their members, you definutly dont want them to be after you, too.