It did not take much to secure the patronage of the United States. The Werwolf Group had a fearsome reputation, as both mercenaries who operated without any verifiable ties to their employers, and with impeccable results nonetheless.
The price was hefty, but as Bruno pointed out, it was significantly cheaper than the cost of raising entire new divisions and equipping them with an invasion of Mexico. It also was an option completely devoid of any political baggage that would normally come with such a thing.
And within weeks, the first Werwolf Mercenaries arrived on Mexico soil, acting as foreign advisors, and agents of foreign internal defense more than anything else. At least on paper that is, underneath the surface however their primary purpose was to foster a local militant faction that was pro-Washington and would be operating under the order of the United States department of defense.