Bill,
I apologize for not being able to answer as quickly as I wanted. Life and a wife who wants a project completed take precedence.
My source for the numbers comes from the "Dictionary of the First World War" by Pen and Sword; UK Publishing. Steven Pope and Elizabeth Anne-Wheal are the Authors from Cambridge and Oxford respectively.
In 1915 the Anglo-French took out guaranteed loans from a consortium of US banks and Industrialists, (Vanderbilt, Getty, ect., ect.). The value of these loans at the time was 500 Million US Dollars. In todays money, a 11.62 Billion dollar loan. By April of 1917 the US banks had extended a further 2.6 Billion in credits. In todays money a further 47.61 Billion.
These loans by my calculation in todays dollars comes to 59.23 Billion USD or 39.39 Billion English Pounds. (This conversion number may move somewhat as we are dealing with "today" monies which move up and down in rates of exchange.)
While the monies were being returned to US firms to pay for contracts at the time of the loans, this still left the banks and Industrialists holding quite a hefty debt. Adding this to the 10.3 billion in imports of food stuffs and other sundries, (239.3 billion in todays USD), you can see why America was heavily invested financially in the Allies winning the war.
Not only had trade suffered and then was suspended with Germany and later its allies compared to the Entente, but retaliation in the form of tariffs and exclusive trade contracts were to be expected from Germany if they won. As it was a standard practice before the war by all the colonial powers why would any reasonable person expect differently post war by a victorious Germany? Especially with one who felt they had an axe to grind.
In game terms a more successful Germany threatening to defeat and render repayment of loans by the Anglo-French, and Russians to a small degree, either haltingly or defaulted all together would drive America to come to their aid quicker. One can make the case that the Zimmerman Telegram was in part sent to try and reduce the monetary and material support that the US was sending to the Anglo French by this time by forcing America to deal with a war on the Southern Frontier.
If you want I would be happy to do a more correct research thesis on the subject as I find the interplay of internal politics in the US at this time quite interesting.
If you want to do the calculations yourself, I used the program at this page for all the conversions. http://www.wolframalpha.com/
Neel