First off, I have not, and will not be messing with Inflation calculations.
Inflation is in Civilization so that you don't get runaway gold income in the later game, and so that larger civilizations don't way outearn smaller civilizations. For the most part, it works fairly well. I would look to other problems (lack of cottages, expensive civics, high city maintainance) for your money woes.
As for the accuracy, 243% inflation is relatively low. In the United States, the inflation from the year 1913 to 2009 is 2085.2%. (I blame our government's run-away spending and minimum wage laws).

also the worst inflation the US had was in the 70s because of Nixon and Ford (though Jimmy Carter had SOME to do with it, not as much as people say)
PS your number reflects compounded interest, while civ doesn't so keep that in mind