Best is always to ask the hotel to ask for a taxi - most are very dependable but you sometimes have the pirate in-between. Borispil to Kiev is some 15 euros (bus is 2 euros) but last year had someone trying to ask me 100 euros :-) Rental cars - they always try to get extra charges (what's new?) and after the car is back, it takes between 2 and 3 weeks to get your money back. Sixt and are the worst offenders.