Most of the hidden costs are buildings I think.. the palace is some 200g and each hut/inn is 50g, pretty sure the other buildings have a gold cost as well. When you mouseover a building icon and the "card" shows up above it, look for the number next to the gold coin symbol, this is the gold you'll instantly lose when you place the building.
I think part of the problem is that the gold costs should not be incurred until the building is actually built - or at least until construction starts. Right now if I "place" 8 huts, I pay for them all at once, even if the 8th hut won't even begin construction for another 20 turns. This:
a.) doesn't make sense (I could've waited 20 turns before placing the 8th hut in the queue, same effect in the end, but the gold is deducted much later - so what happens to that gold for the 20 turns it's not being used?)
b.) creates a big separation between spending the gold and actually getting what you spent that gold on, which makes it much less clear where the gold is actually going. Why am I at -200 gold? Because in 10 turns, after the farm currently being constructed is finished, that gold is going to be spent on a hut. You see, it just doesn't match up.
It'd be much better if it was more like: queue hut to be built (no immediate cost) - 25 turns later when the hut actually gets built, you get a message: "A hut was built in City X, 50g was deducted from the treasury to fund this construction."
