The most g you make from lucky drops in the AH which you might get even in Act 1/INF if you just run enough.
But you can also make some "decent" money just for gold runs etc, there are two i like:
Running Heart of Sin on HELL (!), ultra easy and usually nets 200k-250k each run...or even better Act 1/INF, from "Sword of the Stranger" all the way to butcher. With all items, vendoring etc. i think each run nets about 400k-500k..with the added bonus that you might get the occasional great drop you can sell for lots of M in the AH. So..what i am saying...500k is really VERY easy to make.
Edit: And yes agree that farming Act 3 (let alone 4) Inferno and probably even Act 2 OVERALL is not worth it since Act1 is much, much quicker/easier..which outweighs the benefit of potential better drops in Act3++. (Or, alternatively, my character just plain sucks...at least i am not at a stage yet where i could just "farm" Act 3)