I am not sure that is a cost effective option.
$18 per turn after the initial 2 turns investment of $30.
USA spends 1/3 of their income in their first two turns on setting up Brazil, by which time Germany should have secured the majority of Africa. By the time that the USA makes their first 2 unit landing in Africa on USA 3, Germany will have taken everything with the possible exception of UOSA, and they may have lost Algeria and/or Libya (not a definite with no USA ships in SZ12 to help protect the UK fleet).
So USA then takes turns 4 and 5 to push the Germans back to Egypt (more likely USA 6 if Germany continued to send a few units across the Med). Germany was still net positive income for 6 consecutive turns in Africa, UK income was significantly reduced during that time, and USA was spending nearly half of their income from Turn 3 forward on Africa units.
Yes, the US ends up with a fair number of FIGs shuttling through Africa to Moscow, and it is a good thing too because Germany is going to have Moscow under siege by Turn 6 with so much of the Allied war effort tied up in Africa and UK’s income reduced during the critical early turns.
There simply are cheaper ways for the Allies to re-take Africa that do not jeopardize letting Germany become to powerful on the Eastern Front.