To travel from Berlin and Stockholm there is only one good option, to fly. The flight takes 1½ hours and it’s really easy to find a cheap flight. Here are the most common flight companies and the cheapest tickets found on each airline:
28 euro + booking fee (from Schönefeld to Arlanda)
32 euro + booking fee (from Schönefeld to Arlanda)
13 euro + booking fee (from Schönefeld to Skavsta Airport)
42 euro + booking fee (from Berlin Tegel to Arlanda)
As usual the more time before departure you book the cheaper ticket you will find. For the transfer, the metro in Berlin costs 3 euro to the airport, and from Arlanda to Stockholm you can take a bus for 11 euro. If you fly with RyanAir be prepared that the airport they use are further away from Stockholm then the main Arlanda airport is. The bus transfer when you fly with Ryanair takes 80 minutes from Skavsta Airport (NYO) to Stockholm and cost 14 euro. To pay the ticket use the ticket machines inside the airport, or a VISA card inside the bus (no cash is accepted). Youth tickets are available at a reduced cost for the airport buses from both airports.