That will depend on factors like the amount of people travelling, baggage and where you are going. It could be anything from €15 to €25. There are cheaper alternatives. There is no rail line from...
It depends on the day/traffic. Sunday is most expensive. Usually €20ish but more for extra people and extra bags. If you ask the driver before you get in you might be able to agree to a reduced set...
Dublin Airport is near the city, so it does not take long to get there in normal traffic. Temple Bar is in the city centre. From the airport you could be there in as little as half an hour.