Your question kind of assumes there's one right answer about prices, but really it all depends on when you're looking! Flights from Moscow really are cheaper than from the provinces - there's more competition, more options. Turkish airlines often offer attractive rates, especially on domestic routes or flights to neighboring countries, but I can't give you a specific price because it changes literally every day.
As for hidden catches - the previous answer already correctly pointed out the sneaky fees, and that's definitely a real problem! Check the final cost in your cart before paying, not just the base fare. But I'll add this: sometimes cheap tickets come with awkward dates, layovers, or service classes that barely include anything - no baggage even. A direct route might cost more, but it'll save you hours and headaches.
About booking right now - usually tickets get cheaper about 1.5 to 2 months before departure! If your flight date is already close, there's nothing to catch, just take what you can get. If you've still got time ahead, you can wait, but not forever - at some point prices will go up again. Use price tracking tools to spot the low point!