The Flixbus bus company has been offering shuttle bus transfers from Arland to Stockholm City Terminalen and from Stockholm to the airport, thus becoming another of the cheap alternatives to travel between the international airport and the city center.

FlixBus Shuttle Bus
Shuttle Bus Transfer From Arlanda
FlixBus has stops in Arlanda airport at terminals T2 and T3 as well as at terminal T4 and T5. The journey with FlixBus takes between 40 and 75 minutes and the bus is equipped with free Internet access and power outlets.
The price of a route on the Arlanda – Stockholm line starts at €3.90 / $4.99 / £3.99 and varies depending on demand and departure time. The most expensive I’ve seen cost around €11.90 / $13.99 / £10.99 which is still the cheapest rate.
Buses start operating from Arlanda from 4:05 in the morning until 23:05 at night. The destinations are Solna station (40 min), Stockholm Cityterminalen (55 min) and Liljeholmen (75 min). Not all buses go to the same destination, so you should look carefully which bus is the right one for you. If you want to travel to Stockholm city center then Stockholm Cityterminalen is your destination although you can also travel to Solna and get on the commuter train from there using a public transportation card.
Here you can book your ticket for the shuttle bus departing from:
Transfer From Other Airports in Stockholm
Flixbus also provides some bus transfers from Skavsta (check the link to see if you are lucky) but up until now the best way to travel by shuttle bus from other airports in Stockholm such as Skavsta or Bromma is using the services provided by the Swedish company Flygbussarna.
Finally, from Arlanda airport in Stockholm and from Stockholm City Terminalen you can travel with Flixbus to some 107 destinations in Sweden, Denmark and Germany so this can be a very good way to discover other corners of the country or in Scandinavia.
Transfer From Other Airports in Sweden
It is also possible to travel with FlixBus from Gothenburg-Landvetter airport to Gothenburg city center or from Copenhagen-Kastrup airport to Malmö (one hour).
It is always welcome that there are alternatives that lead to a better service as it fosters competitiveness among the different actors. So welcome be FlixBus!