In my latest Carthage campaign I've decided to send assualt armies the world over to basically roleplay as the US, crush the communist threat in that country, establish military bases all over the place, purchase and train entire native armies, and basically manipulate the world as I see fit, and that takes a mighty big warchest.

add_money 40000 (never had over 40000 appear to work in my game)

(ad infinitum) This is really the only one I use besides fow since a diplomat and waiting a few turns at the latest will almost always get what I want. Highest price tag I've seen was 700k, so keep a good million on hand. The ai doesn't like it when you try to give them a small bribe, then come back with a much larger one.