Despite wonderful advices of nargacugarex, which are mostly coincide with my experience, and for which we should thank him, the whole tourism situation is just a bug/disbalance.
The airport alone won't help much, I've had one :-). And couple of bus depots. And streetcars. And a freaking train staiton. The fact is, at some point, tourists just stop coming by themselves.
So, until I order some shows in Expocenter AND Pro Stadium, which means bringing in around 15000 people for the evening, I'm in red. If I forget to do this one day, or ocassionally do not have enough money for that, I'm bankrupt in one day.
So yeah, in the end you can still be in green by reserving & spending like 60K every day. And you should be pretty lucky (or pretty good planner, as nargacugarex said) just to reach that situation. That, or to build ANOTHER city by yourself to get your first city moving (if that will ever work, of which I'm not sure considering other people's complaints on the forum. Oh gosh)