What is the point of saving the money? Even with biggest empire I would never hit 300 000 limit. Actually playing as romanii on VH/VH in 200 BC I already get 320 000 per turn from my 100 cities, then there are around 260 000 army upkeep expenses per turn, rest 60 000 I use for expansion of towns. So at the end of every turn I usually have 1000 or less.
In this game money (main source of your power) win the war :) So it is pretty bad to keep them in treasury - hurts the whole business - war :)