Staying in Stockholm, Arlanda Express is more expensive than both Heathrow and Oslo, one-way is 260 SEK (28 EUR/22 GBP/38 USD) if bought ahead of the journey, onboard price is 360 SEK (39 EUR/31 GBP/52 USD). Journey time 20 minutes.
As a comparison, Flytoget in Oslo one-way is 170 NOK (21 EUR). Heathrow Express one-way is 21 GBP (ticket machine/online/ticket desk) or 26 GBP (onboard).