score:4
You can take the local bus 579 or 583 to MΓ€rsta station and take the commuter train from there. This is much cheaper than the airport coach or taking the commuter train directly from Arlanda, the current price is 39 SEK. You can pay by touching your credit card on the reader on the bus and on the train station.
The schedules are available on https://sl.se/, they seem to only be available in Swedish. For instance you can search for a journey from "Arlanda terminal 2 och 3 (Sigtuna)" to "Stockholm City (Stockholm)". The buses leave every 30 minutes and the journey takes a little over one hour.
Upvote:1
You can use SJ.se to look up trains and buses from Arlanda to Stockholm.
Rates vary but the cheapest seems to be the bus at 149 SEK (about 14 EUR). Commuter trains start at 181 SEK, with regional trains at 214 SEK.
Note that Arlanda Express trains depart from Arlanda North or South while the other trains depart from Arlanda Central (know as Arlanda C), under Sky City.
The bus and commuter trains also take a lot longer (up to 48 minutes against 20 for the Express and regional trains).