Smedley Butler claimed we used American military power at the behest of corporations in the Caribbean and Latin America. Others, like Stephen Kinzer in "Overthrow", claim that we've gone as far as to oust democratically elected governments solely to install or keep in power ones that are friendly with American business interests. Now none of these ever claim direct evidence to cash in exchange for services compared to say a PMC like Blackwater (Xe, Academi, etc).

EDIT: I mistakenly cited "War Is A Racket" as being about the Banana Wars when it was more focused on war profiteering in WWI.