I don't remember the exact amount, but it's literally a few Euros. I want to say less than €5, but don't remember exactly.
And in my experiences, taxis are VERY unsafe! They will rip you off at every chance. When you land, a million random people will accost you to try and give you a ride somewhere, and those are people you want to avoid.
My suggestion (and what I do every single time): Clear customs etc., and go into the arrival hall. Right in front of you, you'll see a few stands for rental cars etc. One will be for "OK Taxi". Go there, tell them where you're going, and pay them the fee at the desk. They'll give you a receipt with your taxi number and show you where to wait.
No haggling, no cash, no being accosted by randoms.
It's the only possible way I'd consider taking a cab outside the airport.
If you pick any other cab from the street, good luck!
On your return - same story. Ask the hotel to order you a proper taxi. Grabbing one off the street puts you at the drivers mercy.
Good luck!