Nobody can honestly quote you universal numbers because fares differ wildly between countries and even between cities in the same country, so treat any figure a stranger quotes at the airport with suspicion until you have a baseline. The good news is that baselines are easy to get. Ride-hailing apps show a fare estimate before you book even if you end up taking a street taxi, and that estimate is the single most useful pricing anchor you can have.
Airports often publish official fixed fares to city zones on boards at the taxi rank or on the airport website, and where those exist they override the meter and remove all guesswork. Train stations to central hotels are usually short metered rides, so the meter flag-fall plus a modest distance charge is normal.
A few cost drivers worth knowing everywhere: night and holiday surcharges, luggage fees in some cities, tolls passed to the passenger, and airport pickup fees. Ask your hotel before arrival what the trip should cost. Front desk staff answer that question daily and will happily tell you the fair local price.