I do believe that the "battle of the gods" scenerio (can't spell today) has every race start out with 30,000 or 300,000 bc (not sure which). Take a look at that file, and you should be able to create custom maps with different amounts of money. As for altering the amount for randomly generated maps, you can't do that to the best of my knowledge.
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Edit:
I did some checking. You can find the battle of the gods scenario at this location (assuming you installed the game in the default path).
C:\Program Files\Stardock\TotalGaming\GalCiv2\Data\English\Scenarios
However, after looking at the file, I'm no longer sure if you are unable to change the starting cash amount for randomly generated maps. Could you check for me?