Distance from Girona airport to Barcelona City Centre is about 100kms. Taking taxi is not recommended as it may cost more. If you drive a car it would take one and half to reach. Taking a bus would be cheapest and easiest way if you are traveling by Ryan flights.
Girona is about 100 Km far from Barcellona: 1 hour and Half by Bus, maybe even less. You can take that bus just outside the airport, you can't miss it.
